What does the period indicate? Periodic group

Consists of vertical rows (groups) and horizontal rows (periods). For a better understanding of the principles of combining elements into groups and periods, we will consider several elements, say, the first, fourth and seventh groups.

Of the above electronic configurations it can be seen that the outer (highest in energy) electron shells of atoms of the same group are filled with electrons in the same way. The elements located in one vertical column of the table belong to one group. Group IVA elements of the periodic table have two electrons in the s orbital and two electrons in the p orbitals. The configuration of the outer electron shell of the atoms of fluorine F, chlorine Cl and bromine Br is also the same (two s- and five p-electrons). And these elements belong to the same group (VIIA). Atoms of elements of the same group have the same structure of the outer electron shell. That is why such elements have similar chemical properties. The chemical properties of each element are determined by the electronic structure of the atoms of this element . This is the fundamental principle of modern chemistry. It is he who underlies the periodic system.

The group number of the periodic system corresponds to the number of electrons in the outer electron shell atoms of the elements of this group. Period number (horizontal row periodic table) coincides with the number of the highest occupied electron orbital. For example, sodium and chlorine are both elements of the 3rd period, and both types of atoms have the highest, filled with electrons, level - the third.

Strictly speaking, the number of electrons in the outer electron shell determines the group number only for the so-called non-transitional elements located in groups with the letter index A.

The electronic structure of atoms determines the chemical and physical properties of elements. And since the electronic structure of atoms repeats through a period, then the properties of the elements also repeat periodically.

The periodic law of D. I. Mendeleev has the following formulation: "the properties of chemical elements, as well as the forms and properties of the simple substances and compounds they form, are in a periodic dependence on the magnitude of the charges of the nuclei of their atoms".

Atom sizes

We should dwell on two more types of information obtained from the periodic table. The first of these is the question of the size (radius) of atoms. If you move down within a given group, the transition to each next element means filling the next higher level with electrons. In group IA, the outer electron of the sodium atom is in the 3s orbital, potassium is in the 4s orbital, rubidium is in the 5s orbital, etc. Since the 4s orbital is larger than the 3s orbital, the potassium atom is larger than sodium atom. For the same reason in each group, the sizes of atoms increase from top to bottom .

When moving to the right in a period, atomic masses increase, but the sizes of atoms, as a rule, decrease. In the 2nd period, for example, the neon atom Ne is smaller than the fluorine atom, which, in turn, is smaller than the oxygen atom.

Electronegativity

Another trend revealed using the periodic table is a regular change in the electronegativity of elements, that is, the relative ability of atoms to attract electrons that form bonds with other atoms. For example, inert gas atoms do not tend to gain or lose electrons, while metal atoms easily donate electrons, and non-metal atoms readily accept them. Electronegativity (the ability to attract, acquire electrons) increases from left to right within a period and from bottom to top within a group. The last group (inert gases) falls out of these regularities.

Fluorine F, located in the upper right corner of the periodic table, is the most electronegative element, while francium Fr, located in the lower left corner, is the least electronegative. The change in electronegativity is also shown by the arrows in the figure. Using this pattern, one can, for example, argue that oxygen is a more electronegative element than carbon or sulfur. This means that oxygen atoms attract electrons to themselves more strongly than carbon and sulfur atoms.

Pauling's first and widely known scale of relative atomic electronegativity ranges from 0.7 for francium atoms to 4.0 for fluorine atoms.

Electronic structure of inert gases

The elements of the last group of the periodic system are called inert (noble) gases. In the atoms of these elements, in addition to helium He, there are eight electrons on the outer electron shell. Inert gases do not enter into chemical reactions and do not form any compounds with other elements (except for very few exceptions). This is because the configuration of eight electrons on the outer electron shell is extremely stable.

Atoms of other elements form chemical bonds in such a way that they have eight electrons on their outer shell. This position is often called octet rule .

1. The number of the period in the Periodic system of D. I. Mendeleev corresponds to

1) the number of energy levels in an atom
2) the number of valence electrons in an atom
3) the number of unpaired electrons in an atom
4) the total number of electrons in an atom

2. The number of electrons in the electron shell of an atom is determined

1) the number of protons
2) the number of neutrons
3) the number of energy levels
4) the value of the relative atomic mass

3. In the series of chemical elements silicon → phosphorus → sulfur decreases

1) the ability of an atom to accept electrons
2) the highest degree of oxidation
3) the lowest degree of oxidation
4) atomic radius

4. For elements of A groups, with increasing atomic number, it decreases

1) atomic radius
2) the charge of the nucleus of an atom
3) the number of valence electrons in atoms
4) electronegativity

5. In the main subgroups of the Periodic system of D. I. Mendeleev from bottom to top, the main properties of metal hydroxides

1) increase
2) decrease
3) do not change
4) change periodically

6. Among the elements of the IVA group, the maximum atomic radius has

1) germanium
2) carbon
3) tin
4) silicon

7. The most pronounced metallic properties of the element

1) Na
2) Mg
3) K
4) Sa

8. Less pronounced non-metallic properties than silicon has an element

1) carbon
2) germanium
3) phosphorus
4) nitrogen

9. The strongest base corresponds to the element

If the periodic table seems difficult for you to understand, you are not alone! Although it can be difficult to understand its principles, learning to work with it will help in the study of natural sciences. To get started, study the structure of the table and what information can be learned from it about each chemical element. Then you can start exploring the properties of each element. And finally, using the periodic table, you can determine the number of neutrons in an atom of a particular chemical element.

Steps

Part 1

Table structure

The periodic table, or periodic table of chemical elements, begins at the top left and ends at the end of the last line of the table (bottom right). The elements in the table are arranged from left to right in ascending order of their atomic number. The atomic number tells you how many protons are in one atom. In addition, as the atomic number increases, so does the atomic mass. Thus, by the location of an element in the periodic table, you can determine its atomic mass.

As you can see, each next element contains one more proton than the element preceding it. This is obvious when you look at the atomic numbers. Atomic numbers increase by one as you move from left to right. Since the elements are arranged in groups, some table cells remain empty.
- For example, the first row of the table contains hydrogen, which has atomic number 1, and helium, which has atomic number 2. However, they are on opposite ends because they belong to different groups.
Learn about groups that include elements with similar physical and chemical properties. The elements of each group are located in the corresponding vertical column. As a rule, they are indicated by the same color, which helps to identify elements with similar physical and chemical properties and predict their behavior. All elements of a particular group have the same number of electrons in the outer shell.
- Hydrogen can be attributed both to the group of alkali metals and to the group of halogens. In some tables it is indicated in both groups.
- In most cases, the groups are numbered from 1 to 18, and the numbers are placed at the top or bottom of the table. Numbers can be given in Roman (eg IA) or Arabic (eg 1A or 1) numerals.
- When moving along the column from top to bottom, they say that you are "browsing the group".
Find out why there are empty cells in the table. Elements are ordered not only according to their atomic number, but also according to groups (elements of the same group have similar physical and chemical properties). This makes it easier to understand how an element behaves. However, as the atomic number increases, elements that fall into the corresponding group are not always found, so there are empty cells in the table.
- For example, the first 3 rows have empty cells, since transition metals are found only from atomic number 21.
- Elements with atomic numbers from 57 to 102 belong to the rare earth elements, and they are usually placed in a separate subgroup in the lower right corner of the table.
Each row of the table represents a period. All elements of the same period have the same number of atomic orbitals in which electrons are located in atoms. The number of orbitals corresponds to the period number. The table contains 7 rows, that is, 7 periods.
- For example, the atoms of the elements of the first period have one orbital, and the atoms of the elements of the seventh period have 7 orbitals.
- As a rule, periods are indicated by numbers from 1 to 7 on the left of the table.
- As you move along a line from left to right, you are said to be "scanning through a period".
Learn to distinguish between metals, metalloids and non-metals. You will better understand the properties of an element if you can determine what type it belongs to. For convenience, in most tables, metals, metalloids and non-metals are indicated by different colors. Metals are on the left, and non-metals are on the right side of the table. Metalloids are located between them.

Part 2
Element designations
1. Each element is designated by one or two Latin letters. As a rule, the element symbol is shown in large letters in the center of the corresponding cell. A symbol is an abbreviated name for an element that is the same in most languages. When doing experiments and working with chemical equations, the symbols of the elements are commonly used, so it is useful to remember them.
  - Typically, element symbols are shorthand for their Latin name, although for some, especially recently discovered elements, they are derived from the common name. For example, helium is denoted by the symbol He, which is close to the common name in most languages. At the same time, iron is designated as Fe, which is an abbreviation of its Latin name.
2. Pay attention to the full name of the element, if it is given in the table. This "name" of the element is used in normal texts. For example, "helium" and "carbon" are the names of the elements. Usually, though not always, the full names of the elements are given under their chemical symbol.
  - Sometimes the names of the elements are not indicated in the table and only their chemical symbols are given.
3. Find the atomic number. Usually the atomic number of an element is located at the top of the corresponding cell, in the middle or in the corner. It can also appear below the symbol or element name. Elements have atomic numbers from 1 to 118.
  - The atomic number is always an integer.
4. Remember that the atomic number corresponds to the number of protons in an atom. All atoms of an element contain the same number of protons. Unlike electrons, the number of protons in the atoms of an element remains constant. Otherwise, another chemical element would have turned out!
  - The atomic number of an element can also be used to determine the number of electrons and neutrons in an atom.
5. Usually the number of electrons is equal to the number of protons. The exception is the case when the atom is ionized. Protons have a positive charge and electrons have a negative charge. Since atoms are usually neutral, they contain the same number of electrons and protons. However, an atom can gain or lose electrons, in which case it becomes ionized.
  - Ions have electric charge. If there are more protons in the ion, then it has a positive charge, in which case a plus sign is placed after the element symbol. If an ion contains more electrons, it has a negative charge, which is indicated by a minus sign.
  - The plus and minus signs are omitted if the atom is not an ion.