Group 0

Group 0

Known as noble gases, Group 0 consist of helium, neon, argon, krypton, xenon, and radon.
These elements are unreactive due to their full outer shell of electrons.
They are monatomic gases - exist as single atoms.
The boiling points increase down the group due to increase in size of atoms.

Chlorine and Iodine

Both chlorine and iodine are part of Group 7 - the halogens.
Chlorine is a green gas at room temperature whereas iodine is a grey solid.
Both elements form salts with metals.
Chlorine is more reactive than iodine due to its ability to gain an electron more readily.

Alkali Metals

Alkali metals consist of lithium, sodium, potassium, rubidium, cesium, and francium, these metals occupy Group 1 of the periodic table.
All alkali metals have one electron in their outer shell.
They are highly reactive with water and oxygen, reacting more vigorously down the group.
Alkali metals have low melting points compared to most other metals, decreasing down the group.

Electronic Structures of the First 20 Elements

The structure details how electrons are arranged in energy levels or shells around the nucleus of an atom.
The first shell can hold up to 2 electrons, and the second and third can each hold up to 8 electrons.
To be stable, atoms aim to have a full outer shell, often sharing, donating or accepting electrons to achieve this.

Order of Elements in the Modern Periodic Table

Elements are ordered by increasing atomic number.
Rows and columns are known as periods and groups respectively.
Groups contain elements with similar chemical properties and reactions; they have the same number of outer shell electrons.
Periods represent another full set of electron shells.

Atomic Number, Mass Number, Isotope

Atomic number (Z) represents the number of protons in an atom.
Mass number (A) is the sum of the number of protons and neutrons.
Isotopes are atoms of the same element with different numbers of neutrons, hence different mass numbers but same atomic numbers.

Relative Masses and Charges of Protons, Neutrons and Electrons

Protons and neutrons both have a relative mass of 1.
Electrons have a much smaller relative mass, close to 0.
A proton carries a +1 charge, an electron carries a -1 charge, and a neutron is neutral (0 charge).

Atoms

An atom is the smallest part of an element that retains the properties of that element.
Consists of a central nucleus containing protons and neutrons.
Electrons orbit the nucleus in energy levels or shells.
The number of protons equals the number of electrons in an atom, making it overall electrically neutral.