Chapter 1 Atomic structure

Question 1

Structure of an Atom

Answer 1

All matter is composed of atoms which are the smallest parts of an element that can take place in chemical reactions -Atoms are mostly made up of empty space surrounding a very small, dense nucleus that contains protons and neutrons -The nucleus has an overall positive charge due to the presence of these protons -Negatively charged electrons are found in shells in the empty space around the nucleus

Question 2

Subatomic particles

Answer 2

are the particles an element is made up of and include protons, neutrons and electrons These subatomic particles are so small that it is not possible to measure their masses and charges using conventional units (such as grams and coulombs)

Question 3

The atomic number

Answer 3

(or proton number) is the number of protons in the nucleus of an atom and has symbol Z

• The atomic number is equal to the number of electrons present in a neutral atom of an element
• Eg. the atomic number of lithium is 3 which suggests that the neutral lithium atom has 3 protons and 3 electrons

Question 4

The mass number (or nucleon number)

Answer 4

is the total number of protons and neutrons in the nucleus of an atom and has symbol A

-The number of neutrons can be calculated by:

Number of neutrons = mass number – atomic number

-Protons and neutrons are also called nucleons

Question 5

The relative mass

Answer 5

of an electron is almost negligible. -The charge of a single electron is -1.602 x 10-19 coulombs whereas the charge of a proton is -1.602 x 10-19 coulombs, however, relative to each other, their charges are -1 and +1 respectively.

Question 6

Relative mass & charge of subatomic particles table

Answer 6

• subatomic particle: proton, neutron and electron
• relative charge: +1, 0, -1
• relative mass: 1,1,0.0005

Question 7

isotopes

Answer 7

• Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
• The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number

Question 8

Chemical properties of isotopes

Answer 8

• Isotopes of the same element display the same chemical characteristics
• This is because they have the same number of electrons in their outer shells
• Electrons take part in chemical reactions and therefore determine the chemistry of an atom

Question 9

Physical properties of isotopes

Answer 9

• The only difference between isotopes is the number of neutrons
• Since these are neutral subatomic particles, they only add mass to the atom
• As a result of this, isotopes have different physical properties such as small differences in their mass and density

Question 10

Charge Distribution

Answer 10

• The nucleus is also positively charged due to the protons
• Electrons orbit the nucleus of the atom, contributing very little to its overall mass but creating a ‘cloud’ of negative charge
• The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it holds an atom together

Question 11

mass of an atom

Answer 11

• The mass of an atom is concentrated in the nucleus as the nucleus contains the heaviest subatomic particles (the neutrons and protons)
• The mass of the electron is negligible