Topic 1 - Atomic Structure and the Periodic Table

Question 1

What is a compound?

Answer 1

Two or more elements combined chemically in fixed proportions which can be represented by formulae

Question 2

Do compounds have the
same properties as their
constituent elements?

Answer 2

No, they have different properties

Question 3

What is a mixture? Does it have the
same chemical properties as its
constituent materials?

Answer 3

A mixture consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties

Question 4

What are the methods through
which mixtures can be separated
(there are five)? Do these involve
chemical reactions?

Answer 4

Filtration, crystallisation, simple distillation, fractional distillation and chromatography; they do not involve chemical reactions

Question 5

Describe and explain simple
distillation.

Answer 5

Simple distillation is used to separate liquid from a solution – the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid

Question 6

Describe and explain
crystallisation/evaporation

Answer 6

Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent (e.g. salt from H₂O).
The solution is heated until all the solvent evaporates; the solids stays in the vessel.

Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved). Then, we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.

Question 7

Describe and explain
fractional distillation

Answer 7

Fractional distillation is a technique for separation of a mixture of liquids.
It works when liquids have different boiling points.

The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.

The fractionating column contains glass beads. It helps to separate the compounds.In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the column

Question 8

Describe and explain
filtration

Answer 8

Filtration is used to separate an insoluble solid is suspended in a liquid.
The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper.
The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel.

Question 9

Describe and explain
chromatography

Answer 9

Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with the solvent. The solvent level will slowly start to rise, thus separating the spot
(mixture) into few spots (components)

Question 10

What is a separating funnel?

Answer 10

A separatory funnel is an apparatus for separating immiscible liquids.
Two immiscible liquids of different densities will form two distinct layers in the separatory funnel.
We can run off the bottom layer (the liquid with greater density) to a separate vessel

Question 11

Describe the plum-pudding
model

Answer 11

The atom is a ball of positive charge with negative electron embedded in it

Question 12

Describe the Bohr/nuclear
model and how it came
about

Answer 12

The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) – it came about from the alpha scattering experiments

Question 13

Later experiments led to the
discovery of smaller, positive
particles in the nucleus; what are
these particles called?

Answer 13

Protons

Question 14

What did the work of James
Chadwick provide evidence
for?

Answer 14

The existence of neutrons in the nucleus

Question 15

Describe the structure of an
atom

Answer 15

The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons

Question 16

State the relative masses and
relative charges of the proton,
neutron and electron

Answer 16

Masses: 1, 1, very small ; Charges: 1, 0 , -1 (respectively)

Question 17

Explain why atoms are
electrically neutral

Answer 17

They have the same number of electrons and protons

Question 18

What is the radius of an
atom?

Answer 18

0.1 nm

Question 19

What is the radius of a nucleus and
what is it compared to that of the
atom?

Answer 19

1 x 10^-14 m and 1/10000

Question 20

What name is given to the
number of protons in the
nucleus?

Answer 20

Atomic number

Question 21

Atoms of the same element have
the same number of which particle
in the nucleus?

Answer 21

Protons

Question 22

Where is the majority of
mass of an atom?

Answer 22

The nucleus

Question 23

What is the mass number?

Answer 23

The total number of protons and neutrons

Question 24

How does one calculate the
number of neutrons using mass
number and atomic number?

Answer 24

Subtract the atomic number from the mass number

Question 25

What is an isotope? Do isotopes of a certain element have the same chemical properties?

Answer 25

Atoms of the same element (same proton number) that have a different number of neutrons. They have the same chemical properties as they have the same electronic structure

Question 26

What is the relative atomic mass?

Answer 26

The average mass value which takes the mass and abundance of isotopes of an element into account, on a scale where the mass of ¹²C is 12

Question 27

Give the electronic configurations of He (2), Be (4), F (9), Na (11), and Ca (20) to demonstrate how shells are occupied by electrons.

Answer 27

2 2,2 2,7 2,8,1 2,8,8,2

Question 28

What are ions?

Answer 28

Ions are charged particles. They are formed when atoms lose electrons (positive ions) or gain (negative ions) electrons. E.g. sodium positive ion, Na⁺, has an electronic configuration of 2,8 (same as Ne). An atom of sodium has lost one electron

Question 29

Compare the properties of metals and non-metals

Answer 29

Question 30

What is formed when a metal reacts with a non-metal?

Answer 30

An ionic compound (made of positive and negative ions)

Question 31

What is formed when a non-metal reacts with a non-metal?

Answer 31

A molecular compound containing covalently bonded atoms. Atoms share electrons, as opposed to transferring electrons between each other (cf. ionic compounds).

Question 32

Explain the following: solute, solvent, solution, miscible, immiscible, soluble, insoluble.

Answer 32

A solute is a substance that is dissolved in a solvent. Together, they form a solution. Miscible refers to the substances (particularly liquids) that mix together, e.g. water and alcohol. Water and oil are immiscible, i.e. they do not mix. Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in water. Insoluble substance won’t dissolve in a particular solvent.

Question 33

The columns of the periodic table are called…?

Answer 33

Groups

Question 34

The rows of the periodic table are called…?

Answer 34

Periods

Question 35

Are elements in the same group similar or different?

Answer 35

They may have similar chemical properties, as they have the same number of outer shell electrons

Question 36

In terms of energy levels, what are the differences between elements of the same period?

Answer 36

They have the same number of energy levels

Question 37

Electrons occupy particular energy levels, with each electron in an atom at a particular energy level; which available energy level do electrons occupy?

Answer 37

The lowest available energy level

Question 38

The elements of Group 0 are more commonly known as…?

Answer 38

The noble gases

Question 39

What makes the periodic table periodic?

Answer 39

Similar properties of elements occur at regular intervals

Question 40

Elements in the same group have the same number of electrons in their outer shell; what does this tell us about their chemical properties?

Answer 40

They have similar chemical properties

Question 41

In terms of shells, what is the difference between elements in the same period?

Answer 41

They have the same number of shells

Question 42

What change in shell number is seen as one moves down a group?

Answer 42

The number of shells increases

Question 43

Early periodic tables were incomplete and elements were placed in inappropriate groups if what was to be followed?

Answer 43

The strict order of atomic weights

Question 44

Knowledge of what made it possible to explain why the order based on atomic weights was not always correct?

Answer 44

Isotopes

Question 45

Mendeleev overcame some problems with the table by doing what? He also changed the order of some elements based on what?

Answer 45

Leaving gaps; atomic weights

Question 46

The majority of elements are…?

Answer 46

Metals

Question 47

Elements that react to form positive ions are…?

Answer 47

Metals

Question 48

Elements that do not form positive ions are…?

Answer 48

Non-metals

Question 49

Elements in Group 1 are known as…?

Answer 49

The alkali metals

Question 50

State three characteristics of the Alkali Metals

Answer 50

All have one electron in their outer shell; have low density; are stored under oil (to prevent reactions with oxygen or water); are soft (can be cut with knife)

Question 51

How do Group 1 elements react with non-metals? Why are these reactions similar for the different Group 1 elements?

Answer 51

They form ionic compounds which are soluble white solids which form colourless solutions – they all have one electron in their outer shell.

Question 52

How do Group 1 elements react with water?

Answer 52

They release hydrogen and form hydroxides which dissolve to form alkaline solutions; react vigorously with water fizzing and moving around on the surface of the water.

Question 53

How does the reactivity change moving down Group 1? Why?

Answer 53

Reactivity increases as the atoms get larger and the distance between the nucleus and the outer electrons increases and thus attraction from the nucleus decreases, allowing them to more easily lose electrons.

Question 54

State five characteristics of Group 7

Answer 54

- 7 electrons in outer shell - Coloured vapours - Diatomic molecules - Form ionic salts with metals - Form molecular compounds with non-metals

Question 55

State Group 7 elements and their states of matter

Answer 55

---- Fluorine, F. F₂ is a pale yellow gas. Chlorine, Cl. Cl₂ is a pale green gas. Bromine, Br. Br₂ is dark brown liquid Iodine, I. I₂ is a grey solid

Question 56

State three changes that occur in Group 7 as one moves down the group

Answer 56

- Higher relative molecular mass - Higher melting and boiling point - Less reactive - less easily gain electrons

Question 57

A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; write the equations and state the colour change seen when chlorine reacts with sodium bromide and when chlorine/bromine reacts with sodium iodide.

Answer 57

Question 58

A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; explain the trend in reactivity of halogens in these reactions

Answer 58

Reactivity decreases down the group. As we go down the group, the atoms get larger, so an incoming electron will be less tightly held by the attractive forces from the nucleus. That’s why Cl₂ displaces Br^– and I^–.

Question 59

Compare Group 1 metals and transition metals

Answer 59

Group 1 metals and transition metals are heat and electricity conductors. They are shiny when polished and form ionic compounds with non metals. Transition metals have higher densities and higher melting points than Group 1 metals. They are less reactive and harder than Group 1 metals

Question 60

State three common characteristics of transition metals

Answer 60

- Ions with different charges - Coloured compounds - Catalytic propertie

Question 61

What is a catalyst?

Answer 61

A catalyst is a chemical substance that increases the rate of a chemical reaction. It is not used up over the course of the reaction.

Question 62

State the colours of flames observed when lithium, sodium, and potassium burn in oxygen

Answer 62

Crimson-red, Li Yellow-orange, Na Lilac, K

Question 63

Describe the properties of noble gases. Discuss the trend in boiling point down the group

Answer 63

Non-metals, gases, low boiling points, unreactive (full outer shell; they don’t easily accept or lose electrons). The boiling point increases down the group, as the atoms get heavier.