Atomic Structure and Bonding

Question 1

Formation of ions (as a result of electron gain or loss)

Answer 1

An ion is a charged atom. During reactions, elements gain or lose electrons. –> anions, cations

Atoms form ions by gaining or losing electrons through electron transfer.

Question 2

Cation

Answer 2

Metal atoms that lose electrons forming positive ions.

Question 3

Anions

Answer 3

Non-metal atoms gain electrons forming negative ions known as anions.

exception: hydrogen = non-metal that forms positive ions.

Question 4

Ionic Bond

Answer 4

The electrostatic force of attraction between oppositely charged ions.

Question 5

Formation of ionic compounds (as a result of electron transfer)

Answer 5

Ionic compounds are formed during a reaction between a metal atom and a non-metal atom. Outer (valent) shell electron(s) are removed from a metal atom by a non-metal atom. The metal atom loses electron(s) forming positively charged ions called cations and the non-metal atom gains electron(s) forming negatively charged ions called anions. The ions are held together by the electrostatic attraction of the oppositely charged ions.

Question 6

Ionic Bonding

Answer 6

e. g.
- Lithium atom donates/transfers electrons to chlorine atom.
- One Lithium atom loses an electron to chlorine.
- One chlorine atom gains an electron from lithium.
- Forming ions Li+ and Cl-.
- There is an electrostatic force of attraction between oppositely charged lithium and chloride ions.
- Forming an ionic bond/electrostatic attractions between oppositely charged ions.

Question 7

Polyatomic Ions

Answer 7

Carbonate: CO3(2-)
Sulfate: SO4(2-)
Hydroxide: OH(-)
Nitrate: NO3(-)
Phosphate: PO4(3-)
Hydrogen Carbonate: HCO3(-)
Ammonium: NH4(+)

Question 8

Reasons for properties of ionic compounds

• High melting and boiling points
• Mostly soluble in water
• Ionic solids do not conduct electricity (they are insulators)
• Conduct electricity when dissolved in water or molten (liquid)
• Brittle
• Hard

Answer 8

• High melting and boiling points: The strong electrostatic forces of attraction between the ions require a lot of heat energy to break.
• Mostly soluble in water: If the ionic compound is soluble, the water molecules are able to break the electrostatic force of attraction between ions because water is polar. The force of attraction between water molecules and ions is stronger than the attraction between ions.
• Ionic solids do not conduct electricity (they are insulators): Ions in a solid ionic compound are not free to move. But in a liquid or solution, ions move past each other and charge can flow, inducing current.
• Conduct electricity when dissolved in water or molten (liquid): As ionic compounds are made of charged ions, they can conduct electricity but only if the ions can move. If it is molten or dissolved, the ions are free to move and carry electrical charge.
• Brittle: When force is applied, the ions in the lattice shift so that like ions repel and the lattice breaks (snaps b/c same charge).
• Hard: Ionic compounds have strong electrostatic forces of attractions between oppositely charged ions.

Question 9

Testing for flame test (metal ions)

Answer 9

Flame test to detect presence of metal ion.

Lithium, Li(+) = Red
Sodium, Na(+) = Intense yellow/orange
Potassium, K(+) = Purple (lilac/violet)
Calcium, Ca(2+) = Brick Red

Question 10

Testing for ammonium, NH4(+) ions

Answer 10

1. add dilute sodium hydroxide solution
2. gently heat
3. if NH4(+) is present, characteristic choking smell produced, The ammonia fumes turn damp red litmus paper or damp universal indicator from red to blue.

Question 11

Testing for carbonate, CO3(2-) ions

Answer 11

1. add dilute hydrochloric acid
2. bubble gas through limewater
3. If CO3(2-) present, limewater turns cloudy.

Question 12

Testing for sulfate, SO4(2-) ions

Answer 12

1. add dilute hydrochloric acid
2. add a few drops of barium chloride solution
3. If SO4(2-) present, a white precipitate forms.

Question 13

Testing for halide ions, Cl(-), Br(-), I(-)

Answer 13

1. add dilute nitric acid
2. then add a few drops of silver nitrate solution
3. If Cl(-) present, white precipitate is formed.
   If Br(-) present, cream precipitate is formed.
   If I(-) present, yellow precipitate is formed.

Question 14

Covalent Bond

Answer 14

A covalent bond is a chemical bond that involves the sharing of valence electron pairs between atoms.

Question 15

Covalent Bonding

Answer 15

A covalent bond forms between non-metal elements (non-metal to non-metal). Only valence electrons are involved in the bonding, so the inner shells are not always drawn in the diagrams (Dot and Cross, Solid Line). Electrons are shared so that each atom has a full outer shell of electrons. Covalent bonds are very strong bonds.

Question 16

Dot and Cross Diagrams

Answer 16

Step 1. Identify which elements you are working with.
Step 2. How many valence electrons? (group number)
Step 3. How many more electrons does each atom need to have 8 in the outer shell?
The pair of electrons in the centre are shared by both valence shells.

Question 17

Structural Formula

Answer 17

Structural formula of covalent compounds:

e.g. HCl: H – Cl

Question 18

Simple molecular structural properties

Answer 18

Low melting and boiling points:
There are intermolecular forces between simple molecules. These intermolecular forces are much weaker than the strong covalent bonds in molecules. When simple molecular substances melt or boil, it is these weak intermolecular forces that are overcome.

Do not conduct electricity:
A substance can conduct electricity if: it contains charged particles, and these particles are free to move from place to place.
Simple molecules have no overall charge, or charged particles that can separate, so simple molecular substances cannot conduct electricity, even when liquid or dissolves in water.

Question 19

Polar Molecules

Answer 19

The negative electrons are held in their shells by the attraction of the positive protons in the nucleus. The nucleus has a pull on the electrons.
The strength of the pull depends on the type of atom.
The electrons shared in a covalent bond are pulled closer to the atom with a stronger nuclear pull.
This produces a slight charge on each side of the bond (represented by the lower case delta and + or -).

Question 20

Allotropes

Answer 20

A different form of the same element in the same state.

e.g. diamond and graphite are allotropes of carbon (C).

Question 21

Allotropes of carbon - Diamond

Answer 21

Diamond is extremely hard and has a high melting point (often used in cutting tools to cut things like bricks and concrete). It is insoluble in water and does not conduct electricity.

Every atom in a diamond is bonded to its neighbours by 4 strong covalent bonds, leaving no free electrons and no ions.
This explains why diamond does not conduct electricity, is hard and has a high melting point.

Question 22

Allotropes of carbon - Graphite

Answer 22

Graphite is insoluble in water. It has a high melting point and is a good conductor of electricity, which makes it suitable material for the electrodes needed in electrolysis. It is also a very slippery material (used in pencil leads because layers easily slide onto the paper, leaving a black mark).

Each carbon atom is bonded into its layer with 3 strong covalent bonds. This leaves each atom with a spare electron, which together form a delocalised ‘sea’ of electrons loosely bonding the layers together. These delocalised electrons can all move along together, making graphite a good electrical conductor.

Question 23

Giant Covalent Structures

Answer 23

Giant covalent structures contain very many (undefined numbers) of atoms, each joined to adjacent atoms by covalent bonds.
The atoms are usually arranged into giant regular lattices, extremely strong structures because of the many bonds involved.

Question 24

Properties of Giant Covalent Structures

Answer 24

Very high melting points: this is because a lot of strong covalent bonds must be broken.

Variable electrical conductivity: Diamond does not conduct electricity, whereas graphite contains free electrons so it does conduct electricity. Silicon is a semi-conductor; it is a midway between non-conductive and conductive.

Question 25

Metallic bonding

Answer 25

Electrostatic attraction between a lattice of metal cations and a sea of delocalized ions.

Question 26

General properties of metals

Answer 26

- High melting and boiling point - Good conductors of heat and electricity - Hard - High density - Malleable - Ductile - Sonorous - Lustrous

Question 27

Alloy

Answer 27

A mixture composed of two or more elements, at least one of which is a metal.

Question 28

How are metals able to conduct electricity?

Answer 28

Delocalized electrons can move through the structure and carry charge.

Question 29

Why are metals malleable?

Answer 29

The arrangement of ions can change but the attraction between cations and delocalized electrons isn't broken.

Question 30

How are metals able to conduct heat?

Answer 30

Delocalized electrons can move faster and pass energy on quickly. The lattice of atoms transmits energy efficiently, as the atoms vibrate and bump into other atoms.

Question 31

Why do metals have a high melting and boiling point?

Answer 31

The electrostatic attractions between cations and delocalized electrons are strong, and it requires lots of heat energy to break them.

Question 32

Intermolecular forces

Answer 32

Intermolecular forces are found between molecules. They are weaker than intramolecular bonds. There are 3 types of intermolecular forces (weakest to strongest force): - Dispersion forces - Dipole-dipole forces - Hydrogen bonds

Question 33

Dispersion

Answer 33

Weakest type of intermolecular bond. They exist between all atoms and molecules. Occur between all molecules due to the constant movement of electrons. At any one instant, there may be more electrons at one end of the molecule than the other (an instantaneous dipole is formed). This is a temporary situation.

Question 34

Dipole-dipole

Answer 34

Some molecules contain atoms with a large difference in nuclear pull. e.g. the chlorine atom has a stronger nuclear pull and therefore the electrons are attracted to the Cl end of the molecule more than the H end. This results in a polar molecule.

Question 35

Hydrogen bonds

Answer 35

This is an 'extra strong' dipole-dipole attraction that occurs between molecules with Hydrogen covalently bonded to a NOF and attracted to a NOF on another molecule. N- Nitrogen O- Oxygen F- Fluorine

Question 36

Boiling and melting points in intermolecular forces.

Answer 36

The properties of molecular substances are determined by their intermolecular forces. These are responsible for boiling point melting point and hardness. The strength of intermolecular forces reflects on the amount of energy it takes to break the bonds between molecules. Molecules that exist as a solid have low kinetic energy and therefore, cannot overcome the intermolecular forces that are holding the molecules together.

Question 37

Boiling point (intermolecular)

Answer 37

With enough kinetic energy, molecules can break the intermolecular forces to exist as a gas. This is known as the boiling point (temperature when a liquid transitions into a gas.)

Question 38

Melting point (intermolecular)

Answer 38

When there is enough energy to overcome the forces the substance transitions into a liquid state. This is known as the melting point (temperature when solid transitions into liquid.)

Question 39

Explain why nitrogen has a low boiling point

Answer 39

(Weak) dispersion forces exist between molecules. | Little energy is needed to break the intermolecular forces.

Question 40

Explain why graphite is soft and is a good conductor of electricity

Answer 40

Graphite has a giant covalent structure. It is a good conductor of electricity as it has delocalized electrons. It is soft b/c layers can slide over one another due to weaker forces