Atoms, Elements & Compounds

Question 1

What are atoms?

Answer 1

• All substances are made of atoms.
• They are the smallest part of an element.
• They cannot be seen with a microscope.

Question 2

Nucleus?

Answer 2

• Is in the middle of the atom, it consists of protons and neutrons.
• Protons are positively charged, neutrons have no charge.
• The overall charge for the nucleus is therefore positive.
• The size of the nucleus is about 1/10,000 of the size of an atom.

Question 3

Electrons?

Answer 3

• Electrons move around the nucleus.
• They are negatively charged and tiny.
• They occupy shells around the nucleus.
• They do not have much mass compared to protons and electrons so nearly all the mass is located in the nucleus.

Question 4

Electrical charge of an atom?

Answer 4

• The number of protons always equals to the number of electrons.
• These charges cancel eachother out, this means the atom has no overall charge.

Question 5

What is an element?

Answer 5

• An element is a substance made up of only one type of atoms.

Question 6

What are compounds?

Answer 6

• Compounds are two or more elements held together by chemical bonds.
• Elements go through chemical reactions to form compounds.

Question 7

Democtrius? 400BC?

Answer 7

• First atomic model
• ‘All matter is made up of invisible particles called atoms, which cannot be destroyed.
• Atomos - indivisible.

Question 8

John Dalton 1800s?

Answer 8

• Second atomic model
• He believed atoms were solid spheres that made up different elements of different sizes.

Question 9

JJ Dalton,1900?

Answer 9

• Third atomic model
• He discovered the electron:
  Since atoms have no overall charge, the atom must have positive charges to cancel out negatice charges.
• He created the Plum Pudding model, where the atom is a ball of positive charge with negative electrons stuck in it.

Question 10

Ernest Rutherford, 1910?

Answer 10

• He proved that there is a small positively charged centre to an atom.
• He fired positive alpha particles at a thin gold sheet. Some were repelled by the centre of the atoms.
• His atomic model consisted of a tiny positive nucleus with all the mass of the atom in the centre, surrounded by a cloud of negative electrons.
• Most of the atom is empty space as most of the particles passed through the atoms.

Question 11

Niels Bohr, 1913?

Answer 11

• He suggested that electrons orbit the nucleus at fixed distances from the nucleus - in shells.

Question 12

Rutherford, 1918?

Answer 12

• Discovered the nucleus contains protons.

Question 13

Chadwick, 1932?

Answer 13

• Identified a second neutral particle in the nucleus - the neutron.

Question 14

What are isotopes?

Answer 14

• Isotopes are atoms of the same element with different numbers of neutrons.

Question 15

Formula for relative atomic mass?

Answer 15

• Relative atomic = sum of (isotope abundance x isotope mass no.)/
  mass (Ar) 100