Atomic Structure and The Periodic Table

Question 1

What is an atom?

Answer 1

smallest part of an atom that can exist

Question 2

What is an element?

Answer 2

substance of only one type of atom

Question 3

How are the elements listed and approximately how many are there?

Answer 3

in periodic table; approx 100

Question 4

Elements can be classified into two groups based on their properties; what are these groups?

Answer 4

metals and non-metals

Question 5

Elements may combine through chemical reactions to form new products; what are these new elements called?

Answer 5

compounds

Question 6

What is a compound?

Answer 6

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

Question 7

Do compounds have the same properties as their constituent elements?

Answer 7

no, they have different properties

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

Describe and explain simple distillation.

Answer 10

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 11

Describe and explain crystallisation.

Answer 11

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 12

Describe and explain fractional distillation.

Answer 12

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 13

Describe and explain filtration.

Answer 13

Filtration is used to separate an insoluble solid that 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 14

Describe and explain chromatography.

Answer 14

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 15

What is a separating funnel?

Answer 15

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 16

Describe the plum-pudding model.

Answer 16

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

Question 17

Describe the Bohr/nuclear model and how it came about.

Answer 17

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

Question 18

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

Answer 18

protons

Question 19

What did the work of James Chadwick provide evidence for?

Answer 19

The existence of neutrons in the nucleus.

Question 20

Describe the structure of an atom.

Answer 20

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

Question 21

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

Answer 21

Masses: 1, 1, very small ; Charges: 1, 0, -1

Question 22

Explain why atoms are electrically neutral.

Answer 22

They have the same number of electrons and protons.

Question 23

What is the radius of an atom?

Answer 23

0.1 nm

Question 24

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

Answer 24

1 x 10 to the minus 14 m and 1/10000

Question 25

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

Answer 25

atomic number

Question 26

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

Answer 26

protons

Question 27

Where is the majority of mass of an atom?

Answer 27

nucleus

Question 28

What is the mass number?

Answer 28

the total number of protons and neutrons.

Question 29

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

Answer 29

Subtract the atomic number from the mass number.

Question 30

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

Answer 30

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 31

What is the relative atomic mass?

Answer 31

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 32

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

Answer 32

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

Question 33

What are ions?

Answer 33

Ions are charged particles. They are formed when atoms lose electrons (positive ions) or gain (negative ions) electrons.

Question 34

Compare the properties of metals and non-metals.

Answer 34

Property: Boiling/melting point = Metals: High , Non-metals: Low. Property: Conductivity = Metals: Heat and electricity , Non-metals: Don't conduct heat, electricity ( with exception of graphite) Property: Appearance = Metals: Shiny , Non-metals: Dull Property: Malleability = Metals: Yes , Non-metals: Brittle Property: Density = Metals: High , Non-metals: Low Property: Oxides = Metals: Basic , Non-metals: Acidic

Question 35

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

Answer 35

An ionic compound ( made of positive and negative ions).

Question 36

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

Answer 36

A molecular compound containing covalently bonded atoms. Atoms share electrons, as opposed to transferring electrons between each other.

Question 37

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

Answer 37

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 38

The columns of the periodic table are called?

Answer 38

groups

Question 39

The rows of the period table are called?

Answer 39

periods

Question 40

Are elements in the same group similar or different?

Answer 40

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

Question 41

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

Answer 41

They have the same number of energy levels.

Question 42

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

Answer 42

The lowest available energy level.

Question 43

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

Answer 43

The noble gases

Question 44

What makes the periodic table periodic?

Answer 44

Similar properties of elements occur at regular intervals.

Question 45

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 45

They have similar chemical properties

Question 46

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

Answer 46

They have the same number of shells

Question 47

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

Answer 47

number of shells increases

Question 48

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

Answer 48

the strict order of atomic weights

Question 49

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

Answer 49

Isotopes

Question 50

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

Answer 50

leaving gaps; atomic weights

Question 51

The majority of elements are ?

Answer 51

metals

Question 52

Elements that react to form positive ions are?

Answer 52

metals

Question 53

Elements that do not form positive ions are?

Answer 53

non-metals

Question 54

Elements in Group 1 are known as?

Answer 54

alkali metals

Question 55

State three characteristics of the alkali metals.

Answer 55

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

Question 56

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

Answer 56

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

Question 57

How do Group 1 elements react with water?

Answer 57

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 58

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

Answer 58

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 59

State five characteristics of Group 7.

Answer 59

- 7 electrons in outer shell - coloured vapours - diatomic molecules - form ionic salts with metals - form molecular compounds with non-metals

Question 60

State Group 7 elements and their states of matter.

Answer 60

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

Question 61

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

Answer 61

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

Question 62

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 62

Cl2 + 2 NaBr → Br2 + 2 NaCl or Cl2 + 2Br- → Br2 + 2 Cl- in this reaction, an orange colour of Br2 would appear Cl2 + 2 NaI → I2 + 2NaCl or Cl2 + 2I- → I2 + 2Cl- Br2 + 2Nal → I2 + 2 NaBr or Br2 + 2I- → I2 + 2Br- in these two reactions, a brown colour of I2 would appear

Question 63

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 63

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 64

Compare Group 1 metals and transition metals

Answer 64

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 65

State three common characteristics of transition metals.

Answer 65

- Ions with different charges - Coloured compounds - Catalytic properties

Question 66

What is a catalyst?

Answer 66

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 67

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

Answer 67

crimson-red = lithium yellow = sodium lilac = potassium

Question 68

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

Answer 68

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 atoms get heavier.