EL1a - Atoms

Question 1

Define the terms -

• Atomic Number
• Mass Number
• Isotope

Answer 1

• Atomic Number is the number of protons in the atom. This defines the element.
• Mass number is the number of protons plus the number of neutrons.
• Isotopes are atoms of an element with the same atomic number but varying numbers of neutrons in the nucleus.

Question 2

What is the relative atomic mass of an electron?

Answer 2

0.00055 or 1/2000

Question 3

Who proposed the plum pudding model of the atom in 1904?

Answer 3

J. J. Thompson.

Unlike Dalton he knew about electrons, showing the atom was made up of smaller particles.

Question 4

Who conducted in 1911 the experiment where particles were fired at gold foil?

Answer 4

Earnest Rutherford

Question 5

What were the 2 key conclusions of Earnest Rutherford’s experiment?

Answer 5

• the positively charged part of the atom must be concentrated in a very dense small space.
• most of the atom is empty space

Question 6

Who first represented the arrangements of electrons around the nucleus with concentric orbits in 1913?

Answer 6

Niels Henrik David Bohr

Question 7

Who created Quantum Theory and discovered that it is impossible to know with certainty both the momentum of an electron and its exact position?

Answer 7

Werner Karl Heisenberg

1901-1976

Question 8

What is Quantum Theory?

Answer 8

Electrons are not particles or waves, but have properties of both and neither.

Question 9

What is the Quantum Model of the atom often called? Why?

Answer 9

Cloud model;
because the position of the electrons is based on probabilities, it is often represented as a cloud showing areas it is likely to find an electron. This is the current understanding of the atom.

Question 10

Who made the following conclusions?

• all matter is made of atoms which cannot be broken down
• all atoms of an element are identical to each other and different to other elements
• atoms are rearranged in a chemical reaction

Answer 10

John Dalton (1766-1844)

Question 11

What was the Rutherford experiment also known as?

Answer 11

Geiger-Marsden

Question 12

Who came up with the first scientific experiments on the atom in 1808?

Answer 12

John Dalton

Question 13

Who, after Bohr’s orbital model, devised the Quantum Mechanical Model in the 1920s?

Answer 13

Erwin Schrodinger (orbitals)

Earnest Rutherford (protons)

James Chadwick (neutrons)