The periodic properties of elements

The electron configuration of chemical elements determines many of their properties.

The periodic properties are the properties of a chemical element which determine its position in the periodic table.

Observe the relative size of the atoms of some elements in the periodic system:

In each group, size increases as the atomic number increases.

In each period, size decreases as the atomic number increases.

Explain why the size of the atoms in a group increases when the atomic number increases.

Look at the electron configuration of the valence shell of elements from group 1 and use this to explain your answer.

As the atomic number of elements in a group increases, the period increases. This means that the valence electrons are in a shell that is further away from the nucleus. In Li they are in shell 2, while in Cs they are in shell 6.

The valence shell determines the size of the atom. The greater the number, the bigger the atom.

Relative Size	Symbol	Z	Electronic configuration	Valence level configuration	Period
●	H	1	1s¹	1s¹	1
●	Li	3	1s² 2s¹	2s¹	2
●	Na	11	1s² 2s²2p⁶ 3s¹	3s¹	3
●	K	19	1s² 2s²2p⁶ 3s²3p⁶ 4s¹	4s¹	4
●	Rb	37	1s² 2s²2p⁶ 3s²3p⁶3d¹⁰ 4s²4p⁶ 5s¹	5s¹	5
●	Cs	55	1s² 2s²2p⁶ 3s²3p⁶3d¹⁰ 4s²4p⁶4d¹⁰ 5s²5p⁶ 6s¹	6s¹	6

Explain why the size of the atoms in a period decreases when the atomic number increases. Use period 2 as an example..

The valence electrons of all the elements in the same period are in the same shell. However, as the atomic number increases, the positive charge of its nucleus also increases. There is more attraction between the nucleus and the valence electrons. Therefore, the size of the atom decreases.

Symbol	Element	Z	Configuration of the valence shell	Group
Ne	Neon	10	2s²2p⁶	18
F	Fluorine	9	2s²2p⁵	17
O	Oxygen	8	2s²2p⁴	16
N	Nitrogen	7	2s²2p³	15
C	Carbon	6	2s²2p²	14
B	Boron	5	2s²2p¹	13
Be	Beryllium	4	2s²	2
Li	Lithium	3	2s¹	1

All atoms, apart from those of the elements in group 18, can be combined with other atoms of the same element or a different element.

The elements in group 18 are known as the noble gases.

The noble gases are stable because they have a full outer valence shell. Their valence electron configuration is s²p⁶ (8 electrons), or 1s² in the case of helium.

The atoms of noble gases are the most stable. The others combine with each other to achieve the same stability.

Atoms that have few electrons in their valence shell tend to lose them, leaving the previous shell complete. As a result, they form positive ions or cations.

This happens with the elements in groups 1, 2, 13 and the transition metals. The ionic charge is the same as the number of electrons lost.

Atom	Electron configuration	Ion	Electron configuration of the ion
Li	1s² 2s¹	Li⁺	1s²
Na	1s2 2s²2p⁶ 3s¹	Na⁺	1s2 2s²2p⁶
Mg	1s² 2s²2p⁶ 3s²	Mg²⁺	1s² 2s²2p⁶
Aℓ	1s² 2s²2p⁶ 3s²3p¹	Aℓ³⁺	1s² 2s²p6

Atoms that have more than four electrons in their valence shell tend to attract the number of electrons they need to reach eight electrons, like the noble gases. As a result, they form negative ions or anions.

Atom	Electron configuration	Ion	Electron configuration of the ion
F	1s² 2s²2p⁵	F⁻	1s² 2s²2p⁶
O	1s² 2s²2p⁴	O²⁻	1s² 2s²2p⁶
N	1s² 2s²2p³	N³⁻	1s² 2s²2p⁶

The metallic character of an element refers to its capacity to lose electrons.

Elements that tend to lose electrons to achieve noble gas configuration are called metals. They form cations.
Elements that tend to gain electrons to achieve noble gas configuration are called nonmetals. They form anions.

The metallic character of elements is a periodic property, as it depends on their position in the periodic table.

All metals in the same group form an ion with the same charge, as they have the same number of valence electrons.
For the same reason, all nonmetals in the same group form an anion with the same charge.

Only the first elements in groups 14 to 18 are nonmetals. As we move down the group, metallic character increases. This is because there is less attraction between the nucleus and the valence electrons due to the increased distance between them.

Semi-metals or metalloids are found between the metals and nonmetals of groups 14 to 18. In terms of electric or thermal conductivity, their behaviour is intermediate. They include many semiconductors that are hugely important for the electronics industry, such as silicon, germanium and arsenic.

The elements in groups 1 and 2 are very reactive metals. They lose their electrons easily, which is why they are typically seen as cations, forming part of compounds.

The majority of metals that we know of are transition elements: Cu, Ag, Au, Hg, etc.

These are less reactive, so they can exist without combining with other elements.

Nearly all metals are shiny solids at room temperature and conduct heat and electricity. These properties differentiate them from non-metallic elements.

We have seen how increases and decreases the size of the atoms.

Look at the image and answer.

Find the following elements in the periodic table.

Fill in the table with the information about their group and period, and classify them as metals or nonmetals

Element	Group	Period	Metal	Nonmetal
Br
Cu
Ni
Aℓ
K
Mg
N
S

The atoms of the noble gases are the most stable. Therefore, other atoms tend to gain or lose electrons in order to obtain the same valence configuration as a noble gas. They can do this by forming an ion, where they acquire a negative or positive charge equal to the number of electrons that each atom gains or loses.

Find the following elements in the periodic table and fill in the information about each one.

Element	Group	Valence electrons	Charge of ion
Li
S
Aℓ
P
N
Mg
Se
Cℓ

Summary. The periodic properties of elements

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