chemical bonding and structure

Question 1

what is an atom?

Answer 1

smallest unit of an element that cannot be broken down into anything simpler by chemical means (eg. calcium atom, carbon atom, oxygen atom

Question 2

what is an ion?

Answer 2

a charged particle that is formed when a single atom or a group of atoms loses or gains electrons. A monatomic ion is formed from a single atom, eg calcium ion, oxide ion. A polyatomic ion is formed from a group of atoms that are covalently bonded, eg hydroxide ion, carbonate ion

Question 3

what is a molecule?

Answer 3

A group of two or more atoms that are covalently bonded, e.g. carbon dioxide molecule (CO2), oxygen molecule (O2)

Question 4

what is an alloy?

Answer 4

An alloy is a mixture of a metal with one or more elements.

Question 5

how would you Draw simple diagrams to show the difference in the arrangement of atoms between copper and
brass?

Answer 5

if the alloy is made up of 2 elements. the element in lower percentage will be drawn as bigger circles.

Question 6

Compare the physical properties of an alloy and a pure metal:
1. melting point
2. electrical conductivity
3. malleability & ductility

Answer 6

alloy:
1. usually lower
2. able to conduct
3. not as malleable and ductile

pure metal:
1. high
2. able to conduct
3. malleable and ductile

Question 7

why is an alloy stronger than pure metal?

Answer 7

In a metal, the regular and orderly arrangement allows the layer of atoms in a pure metal to slide
over each other easily when a force is applied. Alloys have different physical properties from
metals because the atoms of different metals are of a different size and disrupt the regular
arrangement of atoms in the pure metal. In an alloy, the layer of atoms in alloys cannot slide over
each other easily when a force is applied.

Question 8

what are the Reasons for making alloys?

Answer 8

• To make metals stronger and harder e.g. cast iron
• To improve the appearance of metals e.g. white gold, pewter
• To lower the melting points of metals e.g. solder (an alloy of tin and lead)
• To make metals more resistant to corrosion e.g. stainless steel

Question 9

define electronegativity

Answer 9

The electronegativity of an atom is a measure of its ability to attract the electrons in a
covalent bond to itself. The smaller the atomic radius, the more tightly held the valence electrons are to the nucleus, the greater the electronegativity. The larger the electronegativity
value, the more electronegative the atom is.

Question 10

what is the trend of electronegativity (down the grp, across the period)

Answer 10

1) Electronegativity increases across the Period and decreases down the Group.
2) F is the most electronegative atom, followed by O and N.

Question 10

what determines the type of chemical bond formed between them.

Answer 10

It is largely the difference between the electronegativity of the atoms that determines the type
of chemical bond formed between them. Generally, covalent compounds are formed between atoms of similar electronegativity (e.g. CH4) while ionic compounds form between atoms of different electronegativity (e.g. NaF).

Question 10

how is ionic bond formed?

Answer 10

An ionic bond is the electrostatic forces of attraction between oppositely charged ions
which formed as a result of the complete transfer of one or more electrons from one atom to another.

Question 10

when are ions formed for ionic bonding?

Answer 10

When metals react with non-metals, ions are only formed if the overall energy change for the
reaction is favourable. Electrons are transferred from the metal atoms to the non-metal atoms, forming cations and
anions with a stable electronic configuration of noble gas.

Question 11

how do you draw ‘Dot- and-cross’ diagrams of ionic compounds

Answer 11

refer to page 9 of notes

Question 12

what are the 2 types of forces present in molecules?

Answer 12

1) Intramolecular forces
2) Intermolecular forces

Question 13

describe the bonds found in simple molecules

Answer 13

When a substance consisting of simple molecules boils, no covalent bonds within the molecules are broken. The increase in thermal energy overcomes only the weak intermolecular forces, which
require little energy to overcome. Intermolecular forces of attraction can be regarded to be weaker
than metallic bonds, ionic bonds and covalent bonds.

Question 14

what are the two types of intermolecular forces of attraction? (describe them)

Answer 14

1) van der Waals’ forces
- Temporary dipole-induced dipole forces of attractions (present in all molecules)
- Permanent dipole- permanent dipole forces of attractions (present in polar molecules)

2) hydrogen bond (present in molecules with F-H, O-H and N-H bonds)
In general, the stronger the intermolecular forces of attraction, the greater the amount of energy
required to overcome these forces, and hence the higher the melting and boiling points.

Question 15

is hydrogen bonds or van der Waals’ force between molecules stronger?

Answer 15

Hydrogen bonds are stronger than van der Waals’ force between molecules, but weaker than covalent bond between atoms, ionic bond between ions and metallic bond.

Question 16

define hydrogen bond

Answer 16

Hydrogen bond is an electrostatic force of attraction between an electron-
deficient hydrogen atom covalently bonded to a small highly electronegative atom (such
as N, O, F) and the lone pair electrons of a nearby highly electronegative atom (N, O, F atom on another molecule)

Question 17

what are the Effects of hydrogen bonding and describe them

Answer 17

1) Solubility of polar molecules in water
o Due to the polar nature of water molecules, it is capable of dissolving many ionic
substances through ion-dipole attraction.

2) Lower density of ice compared to water
o Each H2O molecule is hydrogen-bonded to four other H2O molecules in a tetrahedral
arrangement.
o A very open structure with empty spaces between the water molecules accounts for ice
being less dense than water at 0°C.
o When heat is applied to the molecules, the molecules gain kinetic energy to break the
hydrogen bonds and cause the crystal to collapse. H2O molecules in liquid state then
pack more closely together in a smaller volume. Hence the water in liquid form has
higher density at 0°C. This explains why water expands on freezing and contracts on
melting.

Question 18

Giant Molecular Structures (also known as macromolecular structure) are atomic structures of which forms of carbons?

Answer 18

(a) coal
(b) graphite
(c) diamond
(d)buckyball
(e) nanotube
(f) graphene.

Question 19

What is the strength of the metallic bond is dependent on? (three factors)

Answer 19

The strength of the metallic bond is dependent on three factors:
1) size of the cation
The smaller the size of the cation, the stronger is the metallic bond.
2) charge of the cation
The larger the charge on the cation, the stronger is the metallic bond.
3) number of valence electrons delocalised in the lattice