Topic 3 - Covalent Substances

Question 1

Covalent Bonds

Answer 1

• covalent bonding is when non-metals share valence electrons to form molecules
• covalent bonds mostly happen for the non-metal elements

Question 2

Octet Rule

Answer 2

More stable = 8 electrons

Question 3

Intramolecular Bonds

Answer 3

bond within the molecule

Question 4

Single covalent bonds

Answer 4

when atoms share two electrons, one from each atom, the covalent bond formed is called a single covalent bond, indicated by a straight line

Question 5

Diatomic Molecules

Answer 5

• two elements of the same or different atoms
• can be hydrogen and Chlorine or oxygen oxygen and so on.

Question 6

Lewis structures: electron dot diagram

Answer 6

show the valence shell electrons as they are involved in bonding

Question 7

Non-Bonding Electrons

Answer 7

The outer-shell electrons that are not involved in bonding are called non-bonding electrons

Question 8

Delocalised Electrons

Answer 8

Electrons are free to move

Question 9

Lone Pairs

Answer 9

Pairs of non-bonding electrons are known as lone pairs

Question 10

Double Covalent Bonds

Answer 10

Two pairs of electrons (four elements in total) are shared between the atoms, rather than just one pair.

Question 11

Triple Covalent Bonds

Answer 11

A triple covalent bond occurs when three electron pairs are shared between two atoms

Question 12

Molecular Compounds

Answer 12

• Diatomic molecules - contain two atoms they can be the same or different
• Polyatomic molecules contain more than two atoms

Question 13

Why diamond is very hard

Answer 13

Carbon atoms in diamond are strongly covalently bonded throughout the structure, leading to a very hard substance.

Question 14

Why diamond is a non-conductor of electricity

Answer 14

Each carbon in diamond bonds with four other carbon atoms, meaning that all electrons are localised in bonding and there are no freely moving charged particles.

Question 15

diatomic molecules

Answer 15

molecules made up of 2 elements

Question 16

Polyatomic Molecules

Answer 16

two single covalent bonds, each containing
a shared electron pair

• four non-bonding electrons on the oxygen
  atom.

Question 17

Shape of Molecules affect…

Answer 17

Molecular shape affects melting point, boiling point, hardness
and solubility.

Question 18

Structural Formula

Answer 18

with lines and no electrons shown

Question 19

What is Electronegativity

Answer 19

Electronegativity is the ability of an atom to attract electrons towards
itself when forming a chemical bond.

Question 20

Non-Polar

Answer 20

Bonds with an equal distribution of bonding electrons
electrons shared equally
symmetrical

Question 21

Polar

Answer 21

Bonds with an imbalanced electron distribution
not shared equally
asymmetrical

Question 22

Pyramidal and Bent are

Answer 22

Asymmetrical

Question 23

Intramolecular bonds

Answer 23

Covalent bonding
Between Element
stronger

Question 24

Intermolecular bonds

Answer 24

Weaker
joining different covalent bond together

Question 25

The strength of intermolecular forces is determined….

Answer 25

by the size, shape and polarity of molecules.

Question 26

Intermolecular Forces

Answer 26

dispersion forces: polar and nonpolar molecules, caused by temporary dipoles

dipole–dipole attraction: polar molecules only

hydrogen bonding

Question 27

Dispersion Forces

Answer 27

The molecular mass increases, the dispersion forces become stronger

Molecules that form long chain will tend have stronger dispersion forces.

The stronger the dispersion forces of a substance, the higher its boiling point.

all polar and non polar

Question 28

Dipole Dipole Attraction

Answer 28

• can only occur in polar molecules
• the more polar a molecule is, the stronger the dipole-dipole attraction

Question 29

Hydrogen bonding only occurs with

Answer 29

Nitrogen, Oxygen, Flourine

Question 30

Hydrogen Bonding

Answer 30

Hydrogen bond is approximately ten times stronger than a dipole–dipole attraction,
but about one-tenth the strength of an ionic or a covalent bond.

Question 31

Allotropes

Answer 31

Some elements can exist with their atoms in several different structural arrangements
called allotropes.

Question 32

Allotropes of Carbon
- Diamond

Answer 32

Covalent Bonds, Dispersion Force

Tetrahedral, Network Lattice Structure

Very High melting point, does not conduct electricity, very hard and rigid, high thermal conductivity

drill tips

Question 33

Allotropes of Carbon
- Graphite

Answer 33

Strong covalent bonds, weak dispersion force

covalent layer lattice

slippery and soft, resistance to heat, high electrical conductivity

Battery electrodes, lubricant

Question 34

Allotropes of Carbon
- Amorphous Carbon

Answer 34

Surface interaction between fine carbon particles

no consistent structure

interaction between the fine carbon particles increases the strength and toughness of the product

flue, printer toner ink

Question 35

Electronegativity

Answer 35

increase left to right and up a group

Question 36

What elements dont follow the octet rule

Answer 36

hydrogen, beryllium, or boron

Question 37

Why does diamond not melt but sublime (solid) - gas

Answer 37

Since the bonding in diamond is of equal strength throughout the lattice, if sufficient heat is supplied to break a covalent bond, all covalent bonds can be broken.
There is no weak bonding in diamonds.