Chemistry F321 AS

Why do isotopes not have different chemical properties?

Chemical properties are decided by electron configuration and isotopes have the same number of electrons, just a different number of neutrons

Describe the difference between C12 and C17

C12 and C17 have 6 protons and 6 electrons but C12 has 6 neutrons when C17 has 11 neutrons

What are the relative charges and relative masses of protons neutrons and electrons?

Relative charge: Electron = -1

Proton = +1

Neutron = neutral

Relative Mass: Electron = negligible

Proton = 1

Neutron = 1

Describe the distribution of mass and charge within an atom

Protons and neutrons in an atom are tightly packed together in the positively charged nucleus. The negatively charged electrons are around the nucleus in certain energy levels

Define atomic number and mass number

Atomic number is the number of protons and electrons in the atom

Mass number is the number of protons and neutrons in the nucleus

What is an isotope?

A species with the same number of protons and electrons but different number of neutrons

What isotope is used as the standard measurement of relative masses?

Carbon 12

Define relative isotopic mass

The relative mass of one atom of that isotope compared to 12th the mass of one C12 atom

Define relative atomic mass

The average weighted mass of one atom of an element compared to 12th the mass of one C12 atom

What is the relative atomic mass of a substance containing 88.2% C12 and 11.8% C14?

88.2 x 12 = 1058.4

11.8 x 14 = 165.2

1058.4 +165.2 = 1223.6

1223.6 / 100 = 12.236

Relative atomic mass = 12.2 (3sf)

Define relative molecular mass

The average weighted mean mass of a molecule compared with 12th the mass of one C12 atom

Define relative formula mass

The average weighted mean mass of one formula unit compared to 12th the mass of one C12 atom

Calculate the relative molecular mass of H2SO4

H2 = 2

S = 32.1

O4 = 16 x 4

= 2 + 32.1 + (16 x 4)

98.1

Calculate the percentage composition of silicon in Silicon oxide SiO2

Mr of Silicon Oxide = 28 + (16 x 2) = 60

Percentage of Silicon = 28/60 x 100 = 47%

Calculate the percentage of water in copper sulphate crystals CuSO4.5H2O

Mr of Copper Sulfate crystals = 63.5 + 32.1 + (16 x 4) + 5(2+16) = 249.6

Mr of Water = 90

90/249.6 x 100 =36.1%

What does the term "mole" mean?

A mole is the amount of substance that contains as many particles as there are atoms in exactly 12g of Carbon 12

What is the Avogadro Constant?

6 x 10^23 - it is the actual number of particles in one mole

What is molar mass?

the mass per mole of a substance

Calculate the molar mass of NaCl

Mr of Na = 23

Mr of Cl = 35.5

23 + 35.5 = 58.5

Molar Mass = 58.3g/mol

Define Empirical Formula

The simplest whole number ratio of atoms of each element present in a compound

Define molecular formula

The actual number of atoms of each element in a molecule

Given that 127g of copper combine with 32g of oxygen, what is the formula of copper oxide?

Mr of Cu = 63.5

Mr of O = 16

Number of Moles = 127/63.5 32/16

=2 =2

Divide by 2

= 1 : 1

= CuO

If the percentage of water in magnesium sulphate crystals is 51.2%, what is n in the formula MgSO4.nH2O?

Formulae MgSO4 H2O

Masses 48.8g 51.2g

Mr 120 18

Number of Moles 48.8/120 51.2/18

= 0.406 = 2.85

Divide by 0.406 =1 mole = 7 moles

Empirical formula MgSO4.7H2O

Analysis shows the empirical formula of a compound to be CH2H2O. Its relative molecular mass is 60. What is its molecular formula?

Relative Molecular Mass = 60

Relative empirical formula mass = 12 +2 + 16 = 30

60/30 = 2

The molecular formula is double the empirical formula

The molecular formula is C2H4O2

Define an acid

An acid is a substance that produces hydrogen ions in solution

What is the formula for hydrochloric, sulfuric and nitric acid?

HCl, H2SO4, HNO3

What are the 3 types of common bases

Metal oxides, metal hydroxides and ammonia

Define an alkali

An alkali is a soluble base that releases OH- ions in aqueous solution

What is the formula for Sodium Hydroxide, Potassium Hydroxide and aqueous ammonia?

NaOH, KOH, NH3

What is a salt?

What is the formula for hydrochloric, sulfuric and nitric acid?

It is a substance produced when the H+ ion of a an acid is replaced by a metal ion of NH4+

HCl, H2SO4, HNO3

What do the terms anhydrous, hydrated and water of crystallisation mean?

What are the 3 types of common bases

Anhydrous means the salt is not associated with water molecules/they have been removed.

Hydrated means the salt is associated with water molecules

The water of crystallisation is the hydrated salts prepared from evaporating soluble salts. It is the water molecules associating with salts.

Metal oxides, metal hydroxides and ammonia

What are the three methods of producing a salt and their products?

Define an alkali

Define a base

An alkali is a soluble base that releases OH- ions in aqueous solution

What is the formula for Sodium Hydroxide, Potassium Hydroxide and aqueous ammonia?

NaOH, KOH, NH3

What is a salt?

It is a substance produced when the H+ ion of a an acid is replaced by a metal ion of NH4+

What do the terms anhydrous, hydrated and water of crystallisation mean?

Anhydrous means the salt is not associated with water molecules/they have been removed.

Hydrated means the salt is associated with water molecules

The water of crystallisation is the hydrated salts prepared from evaporating soluble salts. It is the water molecules associating with salts.

What are the three methods of producing a salt and their products?

Acid + Metal --> Salt + Hydrogen

Acid + Metal Carbonate --> Salt + Water + CO2

Acid + Base --> Salt + Water

Define a base

A base is a substance that readily accepts H+ ions from an acid

What is oxidation and reduction

Oxidation is loss of electrons, reduction is gain of electrons

Give the equation for the reaction between calcium and Hydrochloric acid

Ca + 2HCl --> CaCl2 + H2

Define 1st Ionisation Energy

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions iwth a 1+ charge

Define Second Ionisation energy

The energy required to remove 1 mole of electrons from a gaseous ion with a 1+ charge to form 1 mole of gaseous ions with a 2+ charge

Describe the trend in 1st ionisation energy across period 3

Across period 3 ionisation energy increases as the electrons are added to the same shell but the nuclear charge increases, increasing the pull on each outer electron, decreasing the atomic radius. Therefore more energy is required to remove the outer electron

Explain why aluminium and Sulfur deviate from this general trend

Half filled or fully filled subshells are more stable than other subshells so with Aluminium as the outer electron is added to the 3p subshell, it is easier to remove than with Magnesium having a full 3s subshell, it is harder to remove the outer electrons.

Predict the trend in ionisation energy down group 2

Down group 2 the ionisation energy decreases because the nuclear charge increase is negated by an increase in sheilding and atomic radius. This makes it easier to remove the outer electron as the force of attraction between inner nucleus and outer electron is less due to the sheilding

How many electrons can fill the first 4 shells?

2,8,8,2

What is an orbital?

A region that can hold up to two electrons with opposite spins

How many orbitals make up the s, p and d subshells?

s= 1 orbital

p= 3 orbitals

d= 5 orbitals

How many electrons can the s, p and d subshells hold?

S= 2

P= 6

D= 10

What shape are S and P orbitals?

S is eliptical

P is a figure of 8

What groups are in S, P and D blocks in the periodic table

S = group 1 and 2

P = group 3, 4 ,5 ,6, 7, 8

D = transition metals

What is Ionic Bonding

the electrostatic force of attraction between oppositely charged ions

Define Covalent Bonding

A shared pair of electrons

What is a dative covalent bond?

When both electrons in the bond are from the same atom

What is the formula for nitrate ions, carbonate ions, sulphate ions and ammonium ions?

NO3-

CO3 -2

SO4 -2

NH4 +

What determines the shape of a simple molecule?

It is determined by the repulsion between electron pairs surrounding a central atom and the number of regions of charge density

What kind of electron pair repulsion is the greatest?

Lone pair - lone pair repulsion is the greatest

then Lone pair - bonded pair repulsion

then Bonding pair - bonding pair repulsion

What makes a shape trigonal planar and give an example and a bond angle

3 areas of electron density Boron trichloride 120

What makes a shape tetrahedral and give an example and a bond angle

4 areas of electron density or 3 bonds and 1 lone pair. Methane 109.5

What makes a shape non linear and give an example and bond angle

3 or 4 areas of electron density. Either two lone pairs in Water or a lone pair and 2 linear double bonds as in sulfur dioxide. Angle depends on the shape. Water is 104.5 as it has 4 areas of electron density so is similar to tetrahedral just bent. Sulfur dioxide has angle of 118 as it is similar to trigonal planar with 3 areas of electron density but bent due to lone pair

What makes a shape pyramidal, give an example and a bond angle

4 areas of electron density , ammonia, 107

What makes a shape octahedral, give an example and a bond angle

6 areas of electron density, SF6 90

What shape and bond angle does Carbon Dioxide have?

Linear 180

Define the term electronegativity

The ability of an atom to attract the bonding electrons in a covalent bond

How does a permanent dipole arise?

covalently bonded molecules can have different electro-negativities resulting in the electrons in the bond being pulled closer to the more electronegative atom, resulting in an uneven distribution of charge and a polar bond

What are the 3 types of Intermolecular forces?

Hydrogen bonds

Permanent dipole dipole

Induced dipole dipole (Van der Waals)

Describe the difference in strength of the different intermolecular forces

Hydrogen bonds are the strongest

Permanent dipoles are the next strongest

Induced dipole dipole bonds are the weakest

How does hydrogen bonding occur?

Oxygen has a greater electro-negativity than hydrogen so induces a permanent dipole and has a polar bond. The lone pair on oxygen forms a hydrogen with the delta +ve hydrogen on a neighbouring water molecule. Hydrogen bonds can occur between Hydrogen and either Oxygen, Nitrogen or Fluorine

Explain how induced dipole dipole interactions (Van der Waals) occurs?

In an atom the electrons are constantly moving so at a point, they may be closer to one end than another. This induces a dipole. The electrons in neighbouring molecules are attracted to the delta -ve or repelled by the delta -ve inducing a dipole in neighbouring molecules.

Give 2 anomalous properties of water and explain how this occurs

Ice is less dense than water - hydrogen bonds hold water molecules in a crystalline lattice so molecules are far apart making it less dense

High boiling point - many strong hydrogen bonds in water which must be broken to boil the water which require a large amount of heat

Describe Metallic Bonding

It is the force of attraction between positive metal ions and sea of delocalised electrons

Across period 3, what elements form giant metallic, giant covalent and simple molecular structures?

Na, Mg and Al all form Giant metallic structures

Si forms a giant covalent structure

P, S, Cl and Ar all form simple molecular structures

Explain why Phosphorus has a higher boiling point than Chlorine

Phosphorus has 6 strong covalent bonds to be broken to boil it whereas chlorine only has 1 strong covalent bond. Thus Phosphorus requires more energy to break more bonds

Why does Magnesium have a higher boiling point than Sodium?

Magnesium has a 2+ charge and every atom donates 2 electrons to the sea of delocalised electrons therefore there is a greater force of attraction between the outer electrons and nucleus than in in Sodium where it only has a 1+ charge and donates 1 electron

How are elements in the Periodic Table arranged?

They are arranged according to increasing atomic number, in periods showing repeating trends in physical and chemical properties and in groups having similar physical and chemical properties

What is periodicity?

It is the study of recurring patterns in the periodic table in physical and chemical properties between the periods or groups

Describe the redox reactions of Group 2 elements with Oxygen with equations

Magnesium burns with a bright white flame

Calcium burns with a brick red flame

2Mg +O2 ---> 2MgO

Describe the redox reaction of the group 2 elements with water with an equation as an example

Beryllium has no reaction with water or steam even at red heat.

Magnesium burns in steam to produce magnesium oxide and hydrogen.

Very clean magnesium has a very slight reaction with cold water. The reaction soon stops because the magnesium hydroxide formed is almost insoluble in water and forms a barrier on the magnesium preventing further reaction.

Note: As a general rule, if a metal reacts with cold water, you get the metal hydroxide. If it reacts with steam, the metal oxide is formed. This is because the metal hydroxides thermally decompose (split up on heating) to give the oxide and water.

These all react with cold water with increasing vigour to give the metal hydroxide and hydrogen.

Describe the action of water on oxides of elements in Group 2 and state the approximate pH of any resulting solution

MgO + H2O --> Mg(OH)2

Mg(OH)2 will have a pH of 9

Ca(OH)2 will have a pH of 11

Describe the thermal decomposition of the carbonates of elements in Group 2 and the trend in their ease of decomposition

Thermal decomposition is harder down the group as charge density decrease

CaCO3 ---> CaO + CO2

How is Mg(OH)2 and Ca(OH)2 used in industry?

Describe in terms of Van der Waals the trend in boiling point of I2, Br2 and Cl2