How Atoms React

Grade 9

Its all about the Electrons.

• Every element has its own unique number of protons = Atomic Number.

• Usually the number of protons is balanced by the number of electrons= neutral atom.

• Atoms want to achieve stability.• To achieve stability atoms need to complete

their electron orbits with the maximum number of electron allowed.

Nobel Gases

• The Nobel Gases found on the far right of the periodic table all have completed electron orbits. They have the maximum number of electrons allowed in that orbit.

• Helium has 2 electrons, this fills this orbit and makes Helium a stable atom.

Neon

Argon

Alkali Metals

All Alkali metals have a single electron in an orbit.

Achieving Stability

• In order to achieve stability atoms would like to have filled electron orbits.

• This means that atoms must:• Lose electrons• Gain electrons • Share electrons

Valence Electrons

• The electrons found in the outmost orbit of an atom are known as Valence electrons.

• Valence electrons determine how many chemical bonds an atom will make in order to achieve stability.

• This is known as its bonding capacity.

Metals

• Elements that have 1, 2 or 3 electrons in the outer orbits are metals

• Metals will lose their electrons in these orbits to achieve stability.

• When an atom loses electrons to achieve stability this upsets the balance of charges. There are now more positively charged protons in the nucleus than electrons orbiting that nucleus.

Protons = 3+ + +

Electrons = 3- - -

If Lithium loses 1e-

This now leaves +++ and - -This creates an overall charge of

+1The Lithium atom is now known as an

+ve ION

Cations

• Metals lose up to three electrons to become positively charged ions known as CATIONS.

Mnemonic device• Cations are paws-itive• Ca+ions ‘t’ looks like a ‘+’

Cations are pawsitive.

Sodium Ion.

To identify an ion the atom or symbol is drawn inside parentheses (brackets).

[Na]+

What happens to the size of the ion when an atom loses electrons?

Gets smaller

Non –Metals

• Non- metals have 4,5,6 or 7 electrons in their valence orbits.

• Halogens (with 7 electrons) need only one more electron to complete their orbits.

• Halogens will form Negative IONS as they will now have 1 extra electron orbiting the nucleus

Protons = 17+ + + + ++ + + + ++ + + + +

+ +

Electrons = 18- - - - - - - - - -- - - - -- - -

If Chlorine gains 1e-

This now leaves 17 + and 18-

This creates an overall charge of -1

The Chlorine atom is now known as an –ve ION

Anions

• Non-metals that gain electrons form negative ions.

• Negative ions are known as ANIONS.Mnemonic device: ANION is A Negative Ion

Chloride Ion

[Cl]-

What happens to the size of the ion when an atom gains electrons?

Gets bigger

Ionic BondsElements that lose or gain electrons from bonds known as IONIC bonds.Usually ionic bonds are formed between a metal and a non metal.

Sodium Chloride Magnesium Oxide

Molecular/Covalent Bonds

• Non metals with 4 or more valence electrons can share pairs of electrons to complete the outermost orbits.

• These are known as COVALENT bonds• http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atomic/covalentrev2.sht

ml

H2 Cl2

O2