Chemistry

Question 1

When is an ionic bond formed?

Answer 1

By transfer of electrons from METAL atoms to the more electronegative NON-METAL atoms

Question 2

Cations

Answer 2

Metals form cations, cations have an overall positive charge as they lose electrons (low electronegativity)

Question 3

Anions

Answer 3

Non-metals form anions, anions have an overall negative charge as they gain electrons to obtain a stable outer shell (higher electronegativity)

Question 4

Electronegativity

Answer 4

The ability of an atom to attract electrons

Question 5

Electrovalency

Answer 5

The charge value of an ion (e.g beryllium has 2 electrons in outer shell, to have a stable outer shell beryllium will lose 2 electrons to form a Be2+ ion, therefore electrovalency of beryllium is 2+) - gaining electrons means negative electrovalency

Question 6

Ionic Bonding

Answer 6

The complete transfer of valence electrons between atoms. For example one electron is removed from the valence shell of sodium and accepted by the chlorine atom into its valence shell. Sodium ion (Na+) and chloride ion (CI-), meaning there is an electrostatic attraction (+ and - attracted). As a result sodium chloride (NaCI) is formed.

Question 7

Monoatomic ions

Answer 7

Ions that are made up of one atom e.g. sodium ion Na+

Question 8

Polyatomic ions

Answer 8

Ions that are made up of more than one atom e.g. nitrate ion NO3-

Question 9

Covalent bonding

Answer 9

Molecules are formed between a NON-METAL and a NON-METAL (bond is formed by the sharing of electrons)

Question 10

Single bonds

Answer 10

When a bond is formed by the sharing of two electrons (single covalent bond)

Question 11

Double bonds

Answer 11

Sharing a total of four electrons (or two pairs of electrons), double covalent bond

Question 12

Triple bonds

Answer 12

Sharing of total of 6 electrons (or three pairs of electrons) e.g. two nitrogen atoms, each shares three electrons with the other

Question 13

Octane rule

Answer 13

The octane rule identifies that atoms are most stable when they have eight electrons in their valence shell

Question 14

Electronegativitiy of non-metals (high or low)

Answer 14

Non-metals have high electronegativities so they can attract electrons easily, but don’t give up electrons easily

Question 15

Bonding electrons

Answer 15

electrons shared between the atoms

Question 16

Non-bonding electrons

Answer 16

the outer shell electrons not involved in forming a bond (lone pairs).

Question 17

What happens when a chemical reaction occurs?

Answer 17

The atoms rearrange (change places)

Question 18

Signs of chemical change

Answer 18

• Colour change
• Gas produced (bubbles)
• A solid (precipitate) forms in a solution
• Energy is produced or absorbed in the from of heat, sound or light

Question 19

Law of conservation of mass

Answer 19

States that matter cannot be created or destroyed, but it can change forms. (Meaning the number and type of atoms must be the same for both reactants and products)

Question 20

Exothermic reactions

Answer 20

Chemical reactions that release energy into the surroundings, surroundings are warmer as a result. E.g. burning fuel (product energy is less than energy in reactants, released)

Question 21

Endothermic reactions

Answer 21

Chemical reactions that absorb energy from the surroundings, surroundings are colder as a result E.g. test-tube feels cold (product energy is greater than energy in reactants, absorbed)

Question 22

4 Classes of Chemical Reactions

Answer 22

• Decomposition reactions
• Synthesis reactions
• Single displacement reactions
• Double displacement reactions

Question 23

Decomposition reaction

Answer 23

AB—> A+B (when a single compound breaks down into two or more elements or new compounds)

Question 24

Synthesis reaction

Answer 24

A + B—> AB (When two reactants combine to form one product)

Question 25

Single Displacement Reaction

Answer 25

AB + C —> A + BC (when an element reacts with a compound and takes the place of another element in that compound)

Question 26

Double Displacement Reactions

Answer 26

AB +CD —> AD + CB (when two compounds react, the positive cation and the negative anion of the two reactants switch places, forming two new substances)

Question 27

Type of Double Displacement: Precipitation Reactions

Answer 27

A precipitate reaction is when soluble aqueous solutions react to form an insoluble solid called a precipitate. (solubility rules determine whether a reaction will form a precipitate)

Question 28

Soluble

Answer 28

DISSOLVES (aq)

Question 29

Insoluble

Answer 29

DOES NOT DISSOLVE (s)

Question 30

Combustion

Answer 30

Combustion reactions are those in which a substance reacts with oxygen, and heat is released (General equation= Hydrocarbon + oxygen —> Carbon dioxide + water (+ heat and light))

Question 31

Hydrocarbons

Answer 31

Compounds containing only the elements carbon and hydrogen e.g. methane CH4, ethane C2H6

Question 32

Neutralisation Reactions

Answer 32

When an acid and a base react with each other to produce water and a salt (General equation: Acid + Base —> Water + Salt)

Question 33

How is the salt formed in a neutralisation reaction?

Answer 33

Combine cation (written first) from base and anion (written second) from acid e.g. base sodium hydroxide reacts with sulfuric acid creating sodium sulfate THEN USE IONS CHART to balance charges

Question 34

What are indicators used for?

Answer 34

Used to identify when the neutralisation between an acid and base is complete (the end point is reached when the solution changes colour)