2.1 Elements, compounds and mixtures
1. Name the three types of particles that make up all matter.
Atoms, molecules and ions.
2. What is the definition of an element?
A substance that consists of only one type of atom.
3. How is a compound defined in chemistry?
A substance formed from two or more different elements that are chemically combined.
4. What is a mixture?
Two or more substances that are physically mixed together but not chemically combined.
5. Describe a primary difference between a compound and a mixture regarding how they are joined.
In a compound, the elements are chemically bonded in fixed proportions, whereas in a mixture, the components are physically combined and can be separated by physical means.
2.2 Atomic structure and the Periodic Table
6. Describe the general structure of an atom.
An atom consists of a central nucleus containing protons and neutrons, surrounded by electrons arranged in shells.
7. What particles are found in the nucleus of an atom?
Protons and neutrons.
8. Where are electrons located in an atom?
In shells surrounding the central nucleus.
9. State the relative charge of a proton, a neutron, and an electron.
A proton has a charge of +1, a neutron has a charge of 0 (neutral), and an electron has a charge of -1.
10. State the relative mass of a proton, a neutron, and an electron.
A proton has a mass of 1, a neutron has a mass of 1, and an electron has a mass that is negligible (approx. 1/1840).
11. Define the term "proton number" (also known as atomic number).
The number of protons in the nucleus of an atom.
12. Define the term "mass number" (also known as nucleon number).
The total number of protons and neutrons in the nucleus of an atom.
13. What is the electronic configuration of an atom with a proton number of 13?
2, 8, 3.
14. What is unique about the electronic configuration of Group VIII noble gases?
They have a full outer electron shell.
15. For elements in Groups I to VII, what is the relationship between the group number and the electronic configuration?
The number of outer shell electrons is equal to the group number.
16. How is the period number of an element related to its electron shells?
The number of occupied electron shells is equal to the period number.
2.3 Isotopes
17. Define "isotopes."
Different atoms of the same element that have the same number of protons but different numbers of neutrons.
18. Why do isotopes of the same element have the same chemical properties?
Because they have the same number of electrons and therefore the same electronic configuration.
19. How is the relative atomic mass of an element calculated?
It is calculated from the relative masses and the percentage abundances of all its isotopes.
2.4 Ions and ionic bonds
20. How is a positive ion (cation) formed?
By an atom losing one or more electrons.
21. How is a negative ion (anion) formed?
By an atom gaining one or more electrons.
22. Define an "ionic bond."
A strong electrostatic attraction between oppositely charged ions.
23. Describe the typical melting and boiling points of ionic compounds.
They have high melting points and high boiling points.
24. Explain why ionic compounds conduct electricity when molten but not when solid.
In the solid state, ions are fixed in a lattice and cannot move;
when molten or in solution, the ions are free to move and carry the electric charge.
2.5 Simple molecules and covalent bonds
25. How is a covalent bond formed?
When a pair of electrons is shared between two atoms, leading to noble gas electronic configurations.
26. Describe the electrical conductivity of simple molecular compounds.
They have poor electrical conductivity because they do not have delocalised electrons or mobile ions to carry a charge.
2.6 Giant covalent structures
27. What are the two giant covalent structures of carbon described in the syllabus?
Graphite and diamond.
28. Why is graphite used as an electrode?
It has delocalised electrons between its layers that allow it to conduct electricity.
29. Why is diamond used in cutting tools?
It is extremely hard because every carbon atom is bonded to four others in a rigid giant covalent lattice.
2.7 Metallic bonding
30. Define "metallic bonding."
The electrostatic attraction between positive ions in a giant metallic lattice and a ‘sea’ of delocalised electrons.
31. Explain why metals are malleable and ductile.
The layers of positive ions can slide over each other without breaking the metallic bond because the delocalised electrons maintain the attraction.