Particle and atomic theory

Question 1

Atoms and size

Answer 1

• Atoms are measured in nanometres.
• A nanometre is one billionth of a metre.
  1nm = 10-9 m = 10-7 cm

Question 2

How to convert metres into mm, um and nm.

Answer 2

m to mm: multiply the length value by 1000

m to um: multiply the length value by 1,000,000

m to nm: multiply the length value by 1,000,000,000

Question 3

Atomic theory

Answer 3

• The nucleus is very small, it is made up of positively charged protons and neutral neutrons.
• The empty space around the nucleus contains negatively charged electrons. These take up most of the space occupied by the atoms.
• Electrons move about the nucleus in orbits. Each electron has a definite energy and moves in a specific energy level.

Question 4

Relative mass of the subatomic particles

Answer 4

Protons and neutrons are 1800x heavier than electrons.

Question 5

The structure of atoms

Answer 5

• Protons, electrons and neutrons are called sub-atomic particles.
• Since atoms are neutrally charged, the number of electrons is the same as the number of protons.
• If an atom gains or loses an electron it becomes charged and is called an ion.
• Atoms are not all the same. To date scientists have identified about 118 different types of atoms.

Question 6

Elements

Answer 6

• Elements are substances that cannot be broken down into simpler substances, containing only one type of atom, e.g. oxygen (O2) contains only oxygen atoms.

Question 7

Compounds

Answer 7

• Compounds consists of two or more different elements chemically combined in fixed proportions.
• The properties of compounds can be very different from the properties of the elements that make them up.

Question 8

Mixtures

Answer 8

• Mixtures are formed when two or more pure substances are combined without them reacting together chemically.
• A mixture can easily be separated into the pure substances that make it up.

Question 9

Molecules

Answer 9

• Atoms can combine together to form molecules. They may be the same type e.g. oxygen O2 or different e.g. carbon dioxide CO2.

Question 10

Atomic number (Z)

Answer 10

• Each element has its own atomic number. The atomic number (Z) is defined as the number of protons in the nucleus of the atom.
• Since all atoms are neutral, the atomic number of an atom will also correspond to the number of electrons in the atom.

Question 11

Mass number (A)

Answer 11

• Protons have about the same mass as neutrons. The mass of electrons is negligible.
• The mass number refers to the number of particles in the nucleus (called nucleons) and equals the number of protons + number of neutrons.

Question 12

Isotopes

Answer 12

• Atoms of a particular element that have the same number of protons, making them the same element, but different number of neutrons thus altering the mass.
• Isotopes have similar chemical properties because their electron structure is the same. They do however, have different physical properties due to their different masses.