Core Knowledge – Topic 1

Topic 1

1) What is an atom?

Answer 1
The smallest particle that has the properties of a chemical element.

2) Describe the structure of an atom.

Answer 2
A nucleus containing protons and neutrons, surrounded by electrons in shells.

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

Answer 3

Protons: mass 1, charge +1

Neutrons: mass 1, charge 0

Electrons: mass almost zero, charge -1.

4) Why do atoms contain the same number of protons and electrons?

Answer 4
Atoms are neutrally charged so they must have the same number of positive particles (protons) as negative particles (electrons)

5) How would you describe the size of the nucleus relative to the rest of the atom?

Answer 5
Very small

6) Where is most of the mass of the atom found?

Answer 6
In the nucleus.

7)What is the mass number of an element?

Answer 7
The total number of protons and neutrons.

8) What is the atomic number of an element?

Answer 8
The number of protons.

9)The number of which particle is unique to an element and gives it its identity?

Answer 9
Protons.

10) If an atom contains 12 protons, how many electrons will it have?

Answer 10
12.

11) If an atom has a mass number of 23 and an atomic number of 11, how many protons, neutrons and electrons does it contain?

Answer 11
protons

11 electrons

23-11 = 12 neutrons

12) What is an isotope?

Answer 12
or more atoms of the same element (the same number of protons) but with a different number of neutrons.

13) What is the relative atomic mass, (Ar)?

Answer 13
The relative mass of an atom compared to the one twelfth mass of an atom of carbon-12.

14) Why do some elements have a relative atomic mass that is not a whole number.

Answer 14
The relative atomic mass is an average mass of all the isotopes that make up the element.

15)What is the formula for calculating relative atomic mass of an element from the relative mass and abundance of its isotopes?

Answer 15

16) How did Mendeleev arrange the elements known at the time into a periodic table?

Answer 16
using the mass number and the properties of the elements and the properties of their compounds of the elements.

17) How did Mendeleev use his table?

Answer 17
To predict the existence and properties of some elements that were still to be discovered.

18)Why does Mendeleev’s method of organising elements in order of increasing atomic mass not always work?

Answer 18
The relative abundancies of some elements isotopes means they can be placed in the wrong place.

19) How are elements in the modern periodic table arranged?

Answer 19
In order of increasing atomic number in rows called periods and elements with similar properties are placed in the same vertical columns called groups.

20) Where are the non-metals found in the periodic table?

Answer 20
At the top on the right hand side.

21) What do all elements in the same row of the periodic table have in common?

Answer 21
They have the same number of shells of electrons.

22)What do all elements in the same column of the periodic table have in common?

Answer 22
have the same number of electrons in their outer shell (and therefore have similar chemical properties).

23)What is an ion? 

Answer 23
charged atom or group of atoms.

24) Describe how an ionic bond is formed.

Answer 24
A metal loses electron(s) to a non-metal. This results in the metal becoming a positively charged ion (cation) and the non-metal a negatively charged ion (anion). These oppositely charged ions then attract.

25)Is a cation positively or negatively charged?

Answer 25
Positive.

26) Is an anion positively or negatively charged?

Answer 26
Negative.

27)What charge do the ions have when formed from elements in group:

  1. 1
  2. 2
  3. 6
  4. 7
Answer 27

  1. +
  2. 2+
  3. 2-
  4. –

28)

What do the compound endings:

  1. ide
  2. ate

mean?

Answer 28

  1. ide – a compound of only the named substances
  2. ate – a compound of the named substances and oxygen

29) What is the formula of the compounds formed from: 

  1. Mg2+ and Cl–
  2. Na+ and O2-?
Answer 29

  1. MgCl2
  2. Na2O

30)Describe the structure of ionic substances.

Answer 30
Ionic substances are a regular arrangement of oppositely charged ions held together in a lattice structure by strong electrostatic forces.

31)How many electrons does Mg2+ have? Mg has an atomic number of 12

Answer 31
10.

32) Describe what happens in covalent bonding?

Answer 32
Two non-metals overlap their outer electron shells and share at least one pair of electrons.

33)What does covalent bonding result in the formation of?

Answer 33
molecules.

34) Name and explain two physical properties of ionic compounds.

Answer 34
  1. They have high melting and boiling points because there are strong electrostatic forces holding the oppositely charged ions in place, therefore a lot of energy is needed to separate the ions.
  2. They can conduct electricity when molten or in aqueous solution (dissolved in water) because the ions are free to move and carry their charge.

35)Name and explain two physical properties of covalent, simple molecular compounds.

Answer 35

  1. They have low melting and boiling points because there are weak intermolecular forces of attraction between molecules.
  2. They do not conduct electricity because the molecules are not charged.

36)

Describe the structures of:

  1. Diamond
  2. Graphite
Answer 36

  1. Each carbon atom is held in place by 4 strong covalent bonds to other carbon atoms. This arrangement is replicated throughout the whole structure creating a giant structure.
  2. Each carbon atom is held in place by 3 strong covalent bonds. This creates flat layers of carbon atoms which stack on top of each other. The unused outer electron on each carbon atom sits between these layers and is delocalised (free to move).

37) Why is diamond used in cutting tools?

Answer 37
Diamond is very hard because all the carbon atoms are joined by 4 strong covalent bonds.

38) Why does diamond have such a high melting point? 

Answer 38
In diamond each carbon atom is held in place by 4 strong covalent bonds and it takes a lot of energy to break these bonds.

39) Why does graphite conduct electricity? 

Answer 39
In graphite each carbon forms 3 bonds, this leaves one electron left over from each carbon atom which sits between the graphite layers and is free to move and carry a charge.

40) Why can graphite act as a lubricant? 

Answer 40
The layers of carbon atoms in graphite are only very weakly joined and are therefore free to slide past each other.

41)What are fullerenes? Explain its properties in terms of its structure and bonding.

Answer 41
C60 is one example where 60 carbons bond together covalently making a structure that looks like a football. These are simple molecules and behave as such (low melting points). However, in C60, carbon forms 3 bonds, the fourth outer electron is delocalised and the molecule conducts electricity. However, there is nothing joining molecules so the conductivity between molecules is poor. Fullerenes are examples of semiconductors.

42) What is graphene? Explain its properties in terms of its structure and bonding.

Answer 42
Graphene is like graphite, just 1 layer thick. It therefore conducts electricity and for its thickness is very strong.

43) Describe polythene’s structure

Answer 43
Polythene is an example of a polymer. It is a large molecule containing chains of carbon atoms surrounded by hydrogen.

44) Describe the bonding in metals? 

Answer 44
All metals form positive ions and their outer electrons are delocalised and sit between the metal ions (forming a ‘sea of electrons’).

45) Why do metals conduct electricity? 

Answer 45
There are free electrons in the metallic structure that can move.

46) Why are metals malleable?

Answer 46
They bend because the ions can slide over one another.

47) Why is it difficult to represent models of compounds on paper?

Answer 47
Compounds are normally 3 dimensional and contain different sized atoms. This can give them particular shapes that are hard to draw clearly in 2 dimensions (on paper).

48) What are the properties of most metals?

Answer 48
Shiny solid, high melting points, high density and good conductors of electricity.

49) What is an empirical formula?

Answer 49
The simplest ratio of the elements in a compound.

50) What is the law of conservation of mass?

Answer 50
During any chemical reaction no particles are created or destroyed. So the overall mass of the reactants must equal the mass of the products.

51)What unit do we use for concentration?

Answer 51
g dm-3 (grams per decimetre cubed).

52) What is 1 mole of particles?

Answer 52
The Avogadro constant (6.02 x 1023 particles).

53) What is the formula to calculate moles?

Answer 53
Moles = Mass/Relative formula mass