Exercises.
1. Fill in the table:
Electronic formula | Number of electrons in the outer level | Number of valence electrons | Characteristic oxidation states. |
|
Manganese | ||||
Aluminum | ||||
2. Make formulas for oxides and determine their type (basic, amphoteric, acidic).
magnesium oxide | zinc oxide | Chromium(III) oxide | Manganese(VII) oxide | lithium oxide | Chromium(VI) oxide |
3. Compare the radii of metals: a) Cu_____Zn, b) Ca_____ Be c) Ca ______Zn.
Metals.
1. Metals are:
1) all s-elements; 2) all p-elements; 3) all d-elements; 4) all elements of the main subgroups.
2. None of the metals:
a) s-elements b) p-elements c) d-elements d) f-elements
1) a, b 2) c, b 3) c, d 4) have everything
3. Atoms in the crystal lattices of metals are held by:
1) ionic bond 2) covalent polar bond 3) hydrogen bond 4) metallic bond
4. Characteristic property of metals:
1) poor thermal conductivity; 2) oxides are ionic;
3) many of them are oxidizers; 4) most oxides are covalent compounds.
5. Metals are characterized by:
1) low thermal and electrical conductivity 2) volatility
3) malleability and ductility 4) under normal conditions, the gaseous state
6. Metal atoms in interaction with non-metal atoms:
1) donate valence electrons 2) accept electrons
3) in some cases they accept electrons, in others they give them away 4) they are oxidizing agents
7. With an increase in the serial number of the metal in the main subgroup, the ability to donate electrons
1) increases 2) does not change 3) decreases 4) increases and then decreases
8.What property is not general for all metals:
1) electrical conductivity; 2) thermal conductivity;
3) solid state of aggregation under standard conditions; 4) metallic luster.
9. Atoms of metals, giving up electrons, acquire the electronic structure of the external energy level:
1) alkali 2) halogens 3) noble gases 4) oxygen
10. The atoms of which metals in the ground state at the energy d-sublevel contain five electrons:
1) Iron 2) Manganese 3) Titanium 4) Vanadium 5) Chromium
11. Among the listed elements, metals include:
1) barium 2) silicon 3) helium 4) boron
12. Which of the groups of elements contains only metals?
1) Li, Be, B 2) K, Ca, Sr 3) Li, Si, Na 4) Se, Te, Po
13. Metallic properties are enhanced in a number of elements
1) sodium - magnesium - aluminum 2) lithium - sodium - potassium
3) barium - calcium - magnesium 4) potassium - sodium - lithium
14. In what series are simple substances arranged in order of increasing metallic properties?
1) Mg, Ca, Ba 2) Na, Mg, Al 3) K, Ca, Fe 4) Sc, Ca, Mg
15. The most pronounced metallic properties are 1) Na 2) K 3) Mg 4) Al
16. 1) Rb 2) Sr 3) Ca 4) K has the least pronounced metallic properties
17. Among the listed metals, select the metal with the least reducing properties: 1) copper 2) lead 3) mercury 4) iron
18. What metals exhibit variable oxidation states: 1) Fe 2) Na 3) Ca 4) Al
19. The oxidation state of chromium in its amphoteric compounds is 1) + 6 2) + 2 3) + 3 4) + 1
20. What kind statements about metals are true:
1) most of the chemical elements are metals
2) metal hydroxides exhibit acidic properties
3) metals are characterized by oxidizing properties
4) metals are poor conductors of electricity
21. What kind statements for metals are incorrect:
1) metals make up the majority of the elements of the Periodic Table;
2) the atoms of all metals at the external energy level contain no more than two electrons; 3) in chemical reactions, metals are characterized by reducing properties;
4) in each period, the alkali metal atom has the smallest radius.
22. In the series sodium - magnesium - aluminum, the elements are arranged in increasing order
1) atomic radius 2) electronegativity
3) metallic properties 4) number of electron layers
23. The metal with the most stable oxidation state +1 is:
1) copper; 2) silver; 3) gold; 4) for all the above metals, the oxidation state +1 is equally stable.
24. Are the following judgments about alkali metals correct?
A. In all compounds, they have an oxidation state of +1.
B. With halogens, they form compounds with ionic bonds.
25. Higher Chromium Hydroxide
1) exhibits acidic properties 2) exhibits basic properties
3) exhibits amphoteric properties 4) does not exhibit acid-base properties
26. Are the following judgments about iron compounds correct?
A. Iron oxide with basic properties corresponds to the formula FeO.
B. For iron (III) hydroxide, only acidic properties are characteristic.
1) only A is true; 2) only B is true; 3) both judgments are true; 4) both judgments are wrong.
27. Are the following judgments about chromium compounds correct?
A. The highest oxidation state of chromium is + 4.
B. Higher chromium oxide is one of the basic oxides.
1) only A is true; 2) only B is true; 3) both judgments are true; 4) both judgments are wrong.
28. Are the following judgments about chromium and iron correct?
A. Both chromium and iron form stable oxides in the +3 oxidation state.
B. Chromium(III) oxide is amphoteric.
1) only A is true; 2) only B is true; 3) both judgments are true; 4) both judgments are wrong.
29. Iron(III) oxide
1) does not show acid-base properties 2) shows acidic properties
3) exhibits basic properties 4) exhibits amphoteric properties
30. Copper(I) compounds in redox reactions
1) do not show any oxidizing or reducing properties
2) exhibit only oxidizing properties
3) exhibit only restorative properties
4) exhibit both oxidizing and reducing properties
Nonmetals.
1. Which of the non-metals is found in free form?
1) silicon; 2) sulfur; 3) chlorine; 4) phosphorus.
2. Atoms of p-elements on the external electronic level have:
1) from one to four s-electrons; 2) from one to five p-electrons;
3) from one to six p-electrons; 4) from one to four p-electrons.
3. Sulfur is an oxidizing agent in reaction with
1) oxygen 2) metals 3) chlorine and fluorine 4) nitric acid
4. The maximum oxidation state of phosphorus in compounds is
1)+6 2)+5 3)+3 4)+4
5. When phosphorus interacts with active metals, compounds are formed in which its oxidation state is 1 + 3 4) + 5
6. In order of strengthening non-metallic properties are
1) S-Se 2) Se-Br 3) Br-I 4) I-Te
7. Non-metallic properties of elements of A groups are enhanced
1) from left to right and in groups from bottom to top 2) from right to left and in groups from top to bottom
3) from right to left and in groups from bottom to top 4) from left to right and in groups from top to bottom
8. the least the energy required to separate an electron from an atom
1) As 2) Se 3) S 4) P
9. the greatest energy must be expended to detach an electron from
1) Ga 2) Al 3) Si 4) C
10. The easiest way to attach electrons is atom 1) sulfur 2) chlorine 3) selenium 4) bromine
11. Attraction of outer layer electrons to the nucleus increases in a row:
1) Si - P - N 2) S - P - As 3) Na - K - Rb 4) Sr - Ca - K
12. In the series of hydrogen compounds of non-metals PH3, H2S, HCl
1) there is no manifestation of acid-base properties
2) basic properties increase, acid properties decrease
3) the acid-base nature of the compounds does not change
4) basic properties decrease, acid properties increase
13. Higher selenium hydroxide 1) H2SeO3 2) H2Se 3) H2SeO4 4) SeO3
14. Are the following judgments about non-metals correct?
A. All non-metal compounds exhibit only oxidizing properties.
B. All hydrogen compounds of non-metals are acids.
15. Are the following judgments about non-metal compounds correct?
A. Oxides formed by non-metal atoms are acidic in higher oxidation states.
B. Volatile hydrogen compounds of all non-metals exhibit acidic properties.
1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
16. Are the following judgments about non-metal compounds correct?
A. All oxides formed by non-metal atoms are acidic.
B. In higher oxidation states, non-metal atoms exhibit oxidizing properties.
1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
17. Are the following judgments about non-metals?
A. In the periodic table, non-metals are located in the right, mainly upper part.
B. There is not a single d-element among non-metals.
1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are wrong
18. Are the following judgments about the elements of the VA group correct?
A. With an increase in the charge of the nucleus, the radius of the atom increases.
B. General formula of the volatile hydrogen compound RH3.
1) only A is true; 2) only B is true; 3) both judgments are true; 4) both judgments are wrong.
19. The strongest oxidizing agent is 1) N2 2) O2 3) F2 4) Cl2
20. Oxides of the composition EO2 and EO3 are formed by each of the two elements:
1) sulfur and selenium 2) nitrogen and phosphorus 3) carbon and silicon 4) iron and chromium
21. Compounds of composition KEO2 and KEO3 form the element 1) nitrogen 2) phosphorus 3) sulfur 4) manganese
22. Formula of higher chlorine hydroxide 1) HCl 2) HClO4 3) HClO3 4) HClO
23. Are the following statements about halogens correct?
A. The oxidizing properties of simple halogen substances increase with an increase in the element's serial number in the Periodic Table of chemical elements.
B. All simple substances halogens are only oxidizing agents.
1) only A is true; 2) only B is true; 3) both judgments are true; 4) both judgments are wrong.
24. With an increase in the ordinal number of an element in a period, the electronegativity of non-metals:
a) is increasing b) decreases; c) first increases, then decreases; d) does not change.
25. The number of electrons on the outer electron layer of non-metal atoms is:
a) period number; c) serial number; b) group number; d) the charge of the nucleus.
General characteristics of non-metals of the main subgroups of IV - VII groups in connection with their position in the periodic system of chemical elements and structural features of their atoms.
1. Are the following judgments about non-metals correct?
A. In the periodic table of chemical elements, all non-metals are located in the main subgroups. B. All non-metals are p-elements.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
2. Under normal conditions, diatomic molecules consist of
1) helium and argon
2) nitrogen and neon
3) sulfur and phosphorus
4) hydrogen and oxygen
3. Are the following judgments about non-metals correct?
A. All non-metals are chemically active substances.
B. Non-metals have only oxidizing properties.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
4. Are the following judgments about non-metals correct?
A. Non-metals form compounds with alkali metals mainly with ionic bonds.
B. Between themselves, non-metals form compounds with a covalent bond.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
5. For atoms of chemical elements located in the row: P-S-C1, increases
2) oxidizing ability
3) recovery ability
4) number of unpaired electrons
6. Compounds of composition NaHEO3 and NaHEO4 can form
1) carbon 2) sulfur 3) chlorine 4) phosphorus
7. The strongest acidic properties are
1) HC1O4 2) H2SO3 3) H3PO4 4) H2SiO3
8) Compounds of composition KEO2 and KEO3 form an element
1) nitrogen 2) phosphorus 3) sulfur 4) manganese
9. Hydrogen exhibits oxidizing properties when reacting with
10. The ability of atoms of chemical elements to accept electrons is enhanced in the series:
1)F -->O -->N
2) N --> F --> O
3) N --> O --> F
4) O -->N -->F
11. The oxidation states of chlorine, bromine and iodine in higher oxides and hydrogen compounds are respectively equal:
1) + 1i-1 2) + 7i-1 3) + 7i-7 4) + 5i-1
12. Sulfur exhibits both oxidizing and reducing properties when interacting with
1) hydrogen and iron
2) carbon and zinc
3) chlorine and fluorine
4) sodium and oxygen
13. In a row: Si --> P --> S --> C1
electronegativity of elements
1) increases
2) decreases
3) does not change
4) first decreases, then increases
14. In the series of elements arsenic --> selenium --> bromine increases
1) atomic radius
2) the number of unpaired electrons in an atom
3) the number of electron layers in an atom
4) electronegativity
15. Hydrogen compound of composition H2E2 forms
1) carbon
2) silicon
16. Are the following statements about halogens correct?
A. The most electronegative among the halogens is iodine.
B. Chlorine is displaced by bromine from aluminum chloride.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
17. Oxygen does not react with
1) water and calcium oxide
2) iron and phosphorus (V) oxide
3) hydrogen and phosphorus (III) oxide
4) hydrogen sulfide and carbon monoxide (IV)
18. The highest hydroxide of an element of group VIIA corresponds to the formula
1) N2EO3 2) N2EO4 3) NEO3 4) NEO4
19. Are the following statements about halogens correct?
A. Fluorine in compounds exhibits both positive and
negative oxidation state.
B. Under normal conditions, bromine and iodine are liquids.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
20. Hydrogen exhibits oxidizing properties when interacting with
1) sodium 2) chlorine 3) nitrogen 4) oxygen
21. Phosphorus exhibits oxidizing properties when interacting with
1) oxygen
2) magnesium
22. Are the following judgments about the properties of sulfur and chlorine correct?
A. The maximum valency of sulfur and chlorine in compounds is equal to the group number.
B. In hydrogen compounds of sulfur and chlorine, the bond is covalent polar.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
23. Phosphorus exhibits oxidizing properties when reacting with
1) calcium 2) sulfur 3) chlorine 4) oxygen
24. When higher chlorine oxide reacts with water, an acid is formed
1) HC1O 2) HC1O2 3) HClO3 4) HClO4
25. The characteristic oxidation states of chlorine in its compounds are:
1) -1, +1, +3, +5, +7
A. Non-metal atoms can participate in the formation of both ionic,
as well as covalent bonds.
B. Non-metal hydroxides are acidic.
1) only A is true
2) only B is true
3) both statements are correct
A. The greater the charge of the nucleus of an atom, the more pronounced its
non-metallic properties.
B. The more pronounced the non-metallic properties of an element, the
its oxide has a more acidic character.
1) only A is true
2) only B is true
3) both statements are correct
A. In the period with an increase in the charges of atomic nuclei,
enhancement of non-metallic properties of elements.
B. In the main subgroup with an increase in the charges of atomic nuclei
there is a weakening of the acidic properties of hydroxides.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong
29. Acid properties are most pronounced in higher hydroxide
2) phosphorus
3) arsenic
30. Nitrogen shows only reducing properties in the compound
Answers: 1-1, 2-4, 3-4, 4-3, 5-2, 6-2, 7-1, 8-1, 9-1, 10-3, 11-2, 12-4, 13-1, 14-4, 15-1, 16-4, 17-1, 18-4, 19-4, 20-1, 21-2, 22-3, 23-1, 24-4, 25- 1, 26-3, 27-2, 28-3, 29-1, 30-2.
There are only 16 non-metal chemical elements, but two of them, oxygen and silicon, make up 76% of the mass of the earth's crust. Non-metals make up 98.5% of the mass of plants and 97.6% of the mass of a person. All the most important organic substances are composed of carbon, hydrogen, oxygen, sulfur, phosphorus and nitrogen; they are the elements of life. Hydrogen and helium are the main elements of the Universe, all space objects, including our Sun, consist of them.
Non-metals are chemical elements whose atoms accept electrons to complete the external energy level, thus forming negatively charged ions. Almost all non-metals have relatively small radii and a large number of electrons in the external energy level from 4 to 7, they are characterized by high electronegativity and oxidizing properties.
If we draw a diagonal from beryllium to astatine in the Periodic system, then non-metal elements will be located upwards on the diagonal to the right, and metals from the bottom left, they also include elements of all secondary subgroups, lanthanides and actinides. Elements located near the diagonal, for example, beryllium, aluminum, titanium, germanium, antimony, have a dual character and are metalloids. Elements of group 18 are inert gases, they have a completely completed outer electron layer, they are sometimes referred to as non-metals, but formally, according to physical characteristics.
Electronic configurations of valence electrons of non-metal elements are given in the table:
Patterns in changing the properties of non-metal elements
In the period with increasing nuclear charge (from left to right):
- the radius of the atom decreases,
- the number of electrons in the outer energy level increases,
- electronegativity increases.
- oxidizing properties are enhanced,
- non-metallic properties are enhanced.
In a group with increasing nuclear charge (from top to bottom):
- the radius of the atom increases,
- the number of electrons in the outer energy level does not change,
- electronegativity decreases.
- oxidizing properties are weakened,
- non-metallic properties are weakened.
Thus, the more to the right and higher the element in the Periodic system, the more pronounced its non-metallic properties.
Non-metals in the main subgroup of group IV of the Periodic Table of D.I. Mendeleev are carbon and silicon. There are 4 electrons in the outer energy level of these elements (ns 2 np 2). In its inorganic compounds, carbon has an oxidation state of +2 (in the unexcited state) and +4 (in the excited state). In organic compounds, the oxidation state of carbon can be any from -4 to +4.
For silicon, the most stable oxidation state is +4. Carbon and silicon form acid oxides of the general formula EO 2 , as well as volatile hydrogen compounds of the general formula EN 4 .
Non-metals in group V of the main subgroup of the Periodic Table of D.I. Mendeleev are nitrogen, phosphorus, arsenic. There are five electrons in the outer energy level of these elements: ns 2 np 3 . Nitrogen in its compounds can show oxidation states -3, -2, +1, +2, +3, +4, +5.
Phosphorus has oxidation states of –3, +3, +5. Since the nitrogen atom does not have a d-sublevel, it cannot be pentavalent, but it is able to form a fourth covalent bond by the donor-acceptor mechanism. With an increase in the serial number within the subgroup, the radii of atoms and ions increase, and the ionization energy decreases. There is a weakening of non-metallic properties and strengthening of metallic ones.
With oxygen, the elements of the main subgroup of group V form higher oxides of the composition R 2 O 5. All of them are acid oxides. With hydrogen, nitrogen, phosphorus, and arsenic form volatile gaseous compounds of the EN 3 composition.
Non-metals of the main subgroup of group VI of the Periodic system D.I. Mendeleev are oxygen, sulfur, selenium and tellurium. The configuration of the external electronic level of these elements is ns 2 np 4 . In their compounds, they exhibit the most characteristic oxidation states -2, +4, +6 (except for oxygen). With an increase in the serial number within the subgroup, the ionization energy decreases, the sizes of atoms and ions increase, the non-metallic features of the elements weaken and the metallic ones increase. Sulfur and selenium form higher oxides of the RO 3 type. These compounds are typical acidic oxides, which correspond to strong acids such as H 2 RO 4 . Non-metals of the main subgroup of group VI are characterized by volatile hydrogen compounds with the general formula H 2 R. In this case, the polarity and bond strength weakens from H 2 O to H 2 Te. All hydrogen compounds, except water, are gaseous substances. Aqueous solutions of H 2 S, H 2 Se, H 2 Te are weak acids.
Elements of group VII of the main subgroup - fluorine, chlorine, bromine, iodine are typical non-metals. The group name of these elements is halogens from the Greek halos - salt and genes - giving birth. The configuration of the external electronic level of these halogens is ns 2 np 5 . The most characteristic oxidation state of halogens is –1. In addition, chlorine, bromine, and iodine can exhibit oxidation states of +3, +5, +7. Within each period, halogens are the most electronegative elements. Within the subgroup, when passing from fluorine to astatine, the atomic radius increases, the non-metallic properties decrease, the oxidative properties decrease and the reduction properties increase. All halogens form simple substances - diatomic Hal 2 molecules. Fluorine is the most electronegative of the chemical elements. In all its compounds, it has an oxidation state of -1. Higher halogen oxides (except fluorine) have the general formula R 2 O 7 and are acidic oxides. They correspond to strong acids of the general formula HRO 4 (R = Cl, Br). Hydrogen compounds of halogens - hydrogen halides have the general formula HHal. Their aqueous solutions are acids, the strength of which increases from HF to HI. For halogens, there is a pattern: each previous halogen is able to displace the next one from its compounds with metals and hydrogen, for example: Cl 2 + 2KBr = 2KCl + Br 2.
The periodic table of Dmitri Ivanovich Mendeleev is very convenient and versatile in its use. It can be used to determine some characteristics of the elements, and, most surprisingly, to predict some properties of chemical elements that have not yet been discovered, not discovered by scientists (for example, we know some properties of the alleged unbihexium, although it has not yet been discovered and synthesized).
What are metallic and non-metallic properties
These properties depend on the element's ability donate or attract electrons. It is important to remember one rule, metals - give electrons, and non-metals - accept. Accordingly, metallic properties are the ability of a certain chemical element to donate its electrons (from an external electron cloud) to another chemical element. For non-metals, the opposite is true. The easier a non-metal accepts electrons, the higher its non-metal properties.
Metals will never accept electrons from another chemical element. This is typical for the following elements;
- sodium;
- potassium;
- lithium;
- France and so on.
The situation is similar with non-metals. Fluorine exhibits its properties more than all other non-metals, it can only attract particles of another element to itself, but under no circumstances will it give up its own. It has the most non-metallic properties. Oxygen (according to its characteristics) comes immediately after fluorine. Oxygen can form a compound with fluorine, giving up its electrons, but it takes negative particles from other elements.
List of non-metals with the most pronounced characteristics:
- fluorine;
- oxygen;
- nitrogen;
- chlorine;
- bromine.
Non-metallic and metallic properties are explained by the fact that all chemicals tend to complete their energy level. To do this, the last electron level must have 8 electrons. The fluorine atom has 7 electrons on the last electron shell, trying to complete it, it attracts one more electron. The sodium atom has one electron on the outer shell, in order to get 8, it is easier for it to give 1, and at the last level there will be 8 negatively charged particles.
Noble gases do not interact with other substances precisely because they have a completed energy level, they do not need to either attract or give away electrons.
How metallic properties change in the periodic system
The periodic table of Mendeleev consists of groups and periods. The periods are arranged horizontally in such a way that the first period includes: lithium, beryllium, boron, carbon, nitrogen, oxygen, and so on. Chemical elements are arranged strictly in order of increasing serial number.
The groups are arranged vertically in such a way that the first group includes: lithium, sodium, potassium, copper, rubidium, silver, and so on. The group number indicates the number of negative particles at the outer level of a certain chemical element. While the period number indicates the number of electron clouds.
The metallic properties are enhanced in the series from right to left or, in other words, weaken in the period. That is, magnesium has greater metallic properties than aluminum, but less than sodium. This is because in the period the number of electrons in the outer shell increases, therefore, it is more difficult for a chemical element to give up its electrons.
In the group, the opposite is true, the metallic properties are enhanced in a row from top to bottom. For example, potassium is stronger than copper, but weaker than sodium. The explanation for this is very simple, the number of electron shells increases in the group, and the farther the electron is from the nucleus, the easier it is for the element to give it away. The force of attraction between the nucleus of an atom and an electron in the first shell is greater than between the nucleus and an electron in the 4th shell.
Let's compare two elements - calcium and barium. Barium ranks lower in the periodic table than calcium. And this means that the electrons from the outer shell of calcium are located closer to the nucleus, therefore, they are better attracted than those of barium.
It is more difficult to compare elements that are in different groups and periods. Take, for example, calcium and rubidium. Rubidium will give off negative particles better than calcium. Because it is below and to the left. But using only the periodic table, it is impossible to unequivocally answer this question by comparing magnesium and scandium (since one element is lower and to the right, and the other is higher and to the left). To compare these elements, special tables will be needed (for example, the electrochemical series of metal voltages).
How non-metallic properties change in the periodic system
Non-metallic properties in the periodic system of Mendeleev change exactly the opposite than metal ones. In fact, these two signs are antagonists.
Strengthen in the period (in a row from right to left). For example, sulfur is less able to attract electrons than chlorine, but more than phosphorus. The explanation for this phenomenon is the same. The number of negatively charged particles on the outer layer increases and therefore it is easier for the element to complete its energy level.
Non-metallic properties decrease in a row from top to bottom (in a group). For example, phosphorus is able to give off negatively charged particles more than nitrogen, but at the same time it is able to attract better than arsenic. Phosphorus particles are attracted to the core better than arsenic particles, which gives it the advantage of an oxidizing agent in reactions to lower and increase the degree of oxidation (redox reactions).
Compare, for example, sulfur and arsenic. Sulfur is higher and to the right, which means that it is easier for her to complete her energy level. Like metals, non-metals are difficult to compare if they are in different groups and periods. For example, chlorine and oxygen. One of these elements is above and to the left, and the other is below and to the right. To answer, we will have to refer to the table of electronegativity of non-metals, from which we see that oxygen more easily attracts negative particles to itself than chlorine.
Periodic table of Mendeleev helps to find out not only the number of protons in an atom, atomic mass and serial number, but also helps to determine the properties of elements.
Video
The video will help you understand the regularities of the properties of chemical elements and their compounds by periods and groups.
