Unit 8

Question 1

Covalent bond

Answer 1

DEFINITION: the electrostatic forces of attraction between the positively charged nuclei of the two bonded atoms and negatively charged shared electrons.
It is formed hence to atoms share a pair of electrons.

1 pair of shared electrons / 1 bond pair of electrons —> single covalent bond

Two hydrogen atoms bond together to make a hydrogen molecule —> diatomic molecule

Question 2

Molecular formula

Answer 2

Gives the total number of atoms of each element present in a molecule of the substance

Question 3

Lone pair of electrons

Answer 3

It is a pair of electrons in the outermost shell of one of the atoms in a molecule which is not involved in bonding.

Question 4

Diatomic molecule

Answer 4

A molecule made up of two atoms bond together

Question 5

How to name covalent compounds?

Answer 5

1. Give the name of the first non-metal and then the second non-metal. (For the second metal, ends it with ide
2. Use prefix mono, di, tri, tetra for one, two, three or four —> mono is only used for the second metal
3. di can be used for the first non-metal

Question 6

Molecular models

Answer 6

1. ball-and-stick model : three-dimensional models where atoms of different elements are represented by different colours and bonds are repented by sticks between balls.
2. space-filling models : three-dimensional models where atoms of different elements are represented by balls of different colours

Question 7

How to predict whether ionic / covalent bond is formed?

Answer 7

When a metal combines with a non-metal, an ionic compound forms. When non-metals combine, a covalent compound forms.

Question 8

Dative Covalent bond

Answer 8

DEFINITION: a type of covalent bond with j which both elect4ons come from the same atom.

Occurrence of dative covalent bonding needs
1. One atom having a lone pair of electrons
2. A second particle having a vacant site in its outermost electron shell to accept the lone pair (ie. a electron-deficient chemical species)

Question 9

Relative molecular mass

Answer 9

For an element or a compound existing as discrete molecules, the relative molecular mass is the sum of the relative atomic masses of all the atoms which make up one molecule

Question 10

Formula mass

Answer 10

used to describe the relative masses of ionic compounds
—> the sum of the relative atomic masses of all the atoms in one formula unit of the compound