Complete pre-IGCSE Chemistry - Theory

Question 1

Define plasma

Answer 1

State formed from extreme heat being applied to a gas, causing electrons to detach from their respective atoms creating a field of positive ions and individual electrons. Can conduct electricity, distinguishing it from gases and very energetic. Overall a neutral electrical charge.

Question 2

True or false - Fluid particles flow due to lower attractive force between each

Answer 2

True for the property and explanation.

Question 3

Name all processes for a substance becoming solid/liquid/gas. Which are endothermic, and how are others exothermic?

Answer 3

a) Melting (solid to liquid), evaporation (liquid to gas), condensation (gas to liquid), freezing (liquid to solid), sublimation (solid to gas), deposition (gas to solid)

b) The first three and sublimation are endothermic. condensation, freezing and deposition are exothermic as they release latent heat more than absorbing it.

Question 4

What state has no fixed properties however expands (spreads evenly) to fill an enclosure?

Answer 4

A gas. The term for spreading is diffusion.

Question 5

Describe particle motion transitioning from one state to another.

Answer 5

Melting, evaporating, subliming all accelerate (speed up) particle motion.

Freezing, condensing, deposition all impede (slow down) particle motion.

Question 6

What causes particle motion? Why is it a bare minimum in solids?

Answer 6

Presence of kinetic energy and peer attract-ability. Solids contain far less of it than any of the other states, especially plasma and gases/particle constituents are very strongly attracted to each other, more so than in gases or liquids.

Question 7

True or false - Phase change is succinct; when ice is melting, the temperature readily increases.

Answer 7

False. Temperature stabilises between melting and boiling points and begins rising again when a phase change has been achieved - i.e. if ice is melting, so long as there are still shards and a puddle temperature remains constant until all shards are liquefied.

Question 8

Compare physical and chemical changes.

Answer 8

Physical changes do not alter the substance identity as its components remain, only in different quantities or state, and tend to be easier to reverse. Chemical change usually involves compound formation, being more difficult to reverse as substance identity has been changed.

Question 9

List examples of each phase change in nature/at home

Answer 9

Check on the internet; sample answers:

Melting - ice cream removed from the freezer
Freezing - Glacier formation
Evaporating - Boiling water with a kettle

Question 10

Name five compounds.

Answer 10

Use Internet to clarify answers. Sample - hydrogen peroxide, sulphuric acid, calcium hydroxide, rust (iron oxide), steel, ammonium nitrate, glucose, sodium chloride, water, acetone, methane, ammonia, carbon dioxide, sodium nitrate, citric acid, sarin

Question 11

List the noble gases

Answer 11

Neon, Argon, Xenon, Helium, Krypton, Radon

Question 12

Compare atomic number and mass number, then provide a formula for calculating atomic mass. Why does atomic mass matter?

Answer 12

a) Atomic number = proton quantity
Mass number = sum of proton + neutron count

b) mass of isotope*abundance in % + result for another isotope, repeat as is necessary/100

c) Atomic mass serves as a reference quality of a given atom to compare its mass with that of another element’s atom, i.e. magnesium atoms weigh about 24 times more than a hydrogen atom, with a relative mass of 1. A value of 12 shows carbon atoms are each half as heavy.

Question 13

Unit for atom size

Answer 13

picometres (pm)

Question 14

3 scientists credited for developing atom theory

Answer 14

Any from John Dalton/Niels Bohr/Erwin Schrödinger/James Chadwick/Max Planck/Ernest Rutherford

Question 15

Examples of a mixture

Answer 15

Air, dyes, saline solution, bag of assorted confectionery, sand; to name a few.

Question 16

Qualities of every subatomic particle (slide 11 lesson 2 PPT)

Answer 16

Protons and neutrons are inside the nucleus, comprising 1 relative mass each. Electrons orbit outside the nucleus, individually 1/1840 of total relative mass

Question 17

Describe methods of displaying electron configuration.

Answer 17

1) Write in shorthand; use x,x,x etc. format (separate no. of electrons per shell with a comma, start another if furthest becomes full. Number of values determines shell count)

2) Create an electron shell diagram - place a dot for the nucleus, draw rings around it and brand x’s atop each ring until complete, repeat until all electrons have been represented.

Question 18

State differences between boiling and evaporation.

Answer 18

• Latter occurs at any temperature as opposed to set;
• Boiling occurs throughout a liquid substance, whereas evaporation is observed at the surface;
• Boiling is faster than evaporation, emitting bubbles where there are none for evaporation; - - Substance does not lose temperature when boiling, but will sometimes when evaporating;
• A dedicated thermal source is required for boiling, however temperature deviation from surroundings naturally causes evaporation

Question 19

Atoms contain _______. These are proton/neutron/electron(s).

Answer 19

Subatomic particles

Question 20

True or False - A tick represents an electron.

Answer 20

Nope. Crosses do

Question 21

Name these elements - 2,8,3/2,8,8/2,1/2,8,6/2,8,8,2

Answer 21

Aluminium, Argon, Lithium, Sulfur, Calcium

Question 22

Which polyatomic ion does not involve an oxygen atom?

Answer 22

Ammonium

Question 23

Define polyatomic ions.

Answer 23

An ion atom formed from two or more elements

Question 24

How are transition metal ions represented?

Answer 24

By placing Roman numerals in brackets, i.e. iron (II) oxide

Question 25

Explain the Periodic Table’s structure, in terms of electronic configuration.

Answer 25

Periods are arranged by how many shells of electrons there are for elements within; groups classify elements by the number of electrons in their outer shell; i.e. Chlorine has 3 shells placing it in period 3, with 7 electrons forming valence.

Question 26

Define valence.

Answer 26

The outer electron shell of an atom.

Question 27

What do +/- indicate, written in superscript to indicate an ion?

Answer 27

+ implies a cation (positive) - the atom has lost electrons; - denotes an anion (negative), electrons have been gained.

Question 28

Effect of ion formation

Answer 28

The atom becomes stable, entering a balanced configuration where no chemical reaction can take place due to every electron shell being full. Likely caused by a previous reaction.

Question 29

Assign each charge to a group from the Periodic Table: +1/2/3, -1/2/3

Answer 29

Group I: +1
Group II: +2
Group III: +3
Group IV: unable to form ions
Group V: -3
Group VI: -2
Group VII: -1