1.2: Atoms, moles and the mole concept

Question 1

What is an atom?

Answer 1

• smallest unit of an element
• contains a nucleus with neutrons and protons, surrounded by orbiting electrons
• An atom has no overall charge

Question 2

What is an element?

Answer 2

• A substance that can’t be broken down into anything simpler by chemical means
• An element contains only one type of atom

Question 3

What is a molecule?

Answer 3

Two or more atoms covalently bonded together

Question 4

What is a compound?

Answer 4

Two or more elements chemically joined together

Question 5

What is an ion?

Answer 5

An atom or group of atoms that have lost or gained one or more electrons and as a result, carry a positive or negative charge

Question 6

What is a chemical equation?

Answer 6

A chemical equation represents a chemical reaction using the formulae of the substances involved. These substances can be elements, compounds and ions.

Question 7

What is a diatomic molecule?

Answer 7

contains 2 atoms covalently bonded together

Question 8

What are the diatomic molecules you need to recall?

Answer 8

• hydrogen
• nitrogen
• oxygen
• fluorine
• chlorine
• bromine
• iodine
• astatine (At)

Question 9

what is the formulae of ozone?

Answer 9

O₃

Question 10

What are the two other elements that have multiple atoms in their molecules?

Answer 10

phosphorus - P₄
Sulfur - S₈

Usually written as just P or S

Question 11

What is the difference with noble gases?

Answer 11

They have 8 electrons in the outer shell which makes them extremely stable.
This means that they are unreactive

Question 12

What is the octet rule?

Answer 12

The tendency of elements to acquire a noble gas electron configuration

Question 13

What ions does the octet rule not apply to?

Answer 13

iron (II) Fe ²+
Cobalt (III) Co³+
Copper (I) Cu+
Manganese (IV) Mn⁴+

Question 14

What is the ionic half-equation of magnesium?

Answer 14

Mg –> Mg²+ + 2e-

Question 15

Ionic half equations and metals

Answer 15

Metals lose one or more electron, so electrons are put on the right-hand side

Question 16

Ionic half equations and non-metals

Answer 16

Non-metals gain one or more electrons, electrons are put on the left-hand side of the equation

Question 17

What are polyatomic ions?

Answer 17

Contain atoms of more than one element bonded together.

Question 18

What are covalent compounds?

Answer 18

Usually made up from two or more non-metal elements

Question 19

What are Ionic compounds?

Answer 19

Usually contain ions of both metal and non-metal elements (exception - ammonium)

Question 20

What does -ate mean when added to an element (e.g. sulfate)

Answer 20

Oxygen is present

Question 21

What does -ite mean when added to an element

Answer 21

oxygen present but LESS than ate

Question 22

What does ‘ium’ mean for ions

Answer 22

Positive ions are formed

Question 23

What is the Ar?

Answer 23

Ar is the average value calculated from the actual masses of isotopes of elements and their relative abundances.

Question 24

How do you calculate Relative atomic mass?

Answer 24

(mass of isotope x %) + (mass of an isotope x %) / 100

Question 25

what is the formula both relative molecular mass and relative formula mass represented by?

Answer 25

Mr

Question 26

How do you calculate Mr?

Answer 26

adding the relative atomic masses found on the periodic table

Question 27

How do you calculate the % by mass of an element?

Answer 27

Total mass of all the atoms of a particular element / Mr of the substance x 100

Question 28

What is a mole?

Answer 28

The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12.

Question 29

What is Avagadro constant?

Answer 29

One mole of substance contains 6.02 x 10²³ particles of that substance

Question 30

What is the molar mass?

Answer 30

The mass of one mole of any substance is the same as its Ar or Mr in grams - measured in gmol-1

Question 31

What are moles used for?

Answer 31

To determine how much product will be made or how much reactant will be needed to complete a reaction

Question 32

How do you calculate moles from mass?

Answer 32

Moles = mass / Mr (or Ar)
n = m/mr

Question 33

How do you calculate the % yield?

Answer 33

% yield = actual moles (mass) / theoretical moles (mass) x 100

Question 34

what is the molar volume?

Answer 34

1 mole of any gas will occupy 24dm³ (24000cm³) at room temp

BECAUSE one mole of any gas contains the same number of particles

Question 35

How do you calculate the volume of gas from moles?

Answer 35

Volume (dm³) = mol x 24dm³³ OR
volume (cm³) = mol x 24000

Question 36

How do you calculate moles from volume of gas?

Answer 36

Moles = volume in (dm³) / 24dm³
OR
Moles = volume in (dm³) / 24000

Question 37

How do you calculate the concentration of a solution?

Answer 37

Conc = moles / vol in dm³

OR

moles = conc x vol in dm³

OR

volume in dm³ = n/c

Question 38

What can concentration also be measured in?

Answer 38

gdm-³

Question 39

How do you change from cm³ to dm³

Answer 39

divide by 1000

Question 40

What can a titration be used for?

Answer 40

To determine the concentration of an acid or base. Titrating known with unknown substance

Question 41

What specialist equipment is used in titrations?

Answer 41

Top pan balance burette
volumetric flask
bulb pipette
burette
tap
conical flask

Question 42

How do you calculate the percentage error overall?

Answer 42

sum of individual percentage errors for each piece of equipment used

% error = uncertainty of apparatus x number of readings / quantity measured x100

Question 43

acid + alkali –>

Answer 43

salt + water

Question 44

What is the empirical formula?

Answer 44

the simplest number ration of the atoms of each element present in a compound

Question 45

What is the molecular formula?

Answer 45

The actual number of atoms of each elements present in a molecule

Question 46

what is the charge on the elements in the periodic table groups - 1,2,3,5,6,7

Answer 46

1: +1
2: +2
3: +3
5: -3
6: -2
7: -1