Chapter 2.1- Atoms and Reactions

Question 1

Early 1800s, Dalton’s atomic theory

Answer 1

Stated that…
Atoms are tiny particles that make up elements
Atoms cannot be divided
All atoms of a given element are the same
Atoms of one element are different from those of every other element

Dalton also used symbols to represent elements and developed the first table of atomic masses

Question 2

1897-1906 Joseph John Thomson and his discoveries

Answer 2

Thomson discovered that cathode rays (recently discovered) were a stream of particles that…
Had a negative charge
Could be deflected by a magnet and an electric field
Had a very small mass

These were electrons. He disproved the theory suggested by the Greek and Dalton

Question 3

What was Thomson’s plum pudding model?

Answer 3

Plum pudding model:
Sea of positive charge with negatively charged electrons on the surface
Charges are balanced

Question 4

1909-11 Rutherford’s gold leaf experiment

Answer 4

Alpha particles directed at a very thin sheet of gold foil
They measured the deflection of these particles

The results…
Most didn’t deflect
Some that did deflect, deflected through large angles
Very few deflected towards the source

Question 5

Rutherford’s new model

Answer 5

The new model stated that…
The positive charge of an atom and most of its mass are concentrated in a central nucleus
Negatively charged electrons orbit around this nucleus
Most of the atom’s volume would be the space between the nucleus and the electrons
Positive and negative charges must balance

Question 6

1913, Niels Bohr’s planetary model

Answer 6

Altered Rutherford’s model to allow electrons to follow only certain paths. Otherwise, electrons would spiral into the nucleus

Question 7

What did Bohr’s model help explain?

Answer 7

Spectral lines seen in emission spectra

Energy of electrons at different distances from the nucleus

Question 8

What did Henry Moseley discover in 1913?

Answer 8

He discovered a link between X-Ray frequencies and an element’s atomic number
Couldn’t explain it at the time

Question 9

Fifth century BCE, Greek Atom

Answer 9

Said that a sample of matter could only be divided a certain number of times
Eventually end up with a particle that doesn’t split

Question 10

What did Rutherford discover in 1918?

Answer 10

The proton

Question 11

What did the discovery of the proton reveal?

Answer 11

It explained Moseley’s finding that an atom’s atomic number was linked to x-ray frequencies
atomic number = number of protons

Question 12

What did Louis de Broglie suggest in 1923?

Answer 12

Particles could have the nature of both a wave and particle

Question 13

What did Schroedinger suggest in 1926?

Answer 13

He suggested that an electron had wave-like properties

Also introduced the idea of atomic orbitals

Question 14

What did Chadwick discover in 1932?

And how did he discover this?

Answer 14

The neutron
He observed a new type of radiation that was emitted from some elements. This radiation was made up of uncharged particles with approximately the same mass as a proton

Question 15

What are protons and neutrons thought to be made up of?

Answer 15

They are thought to be made up of even smaller particles called quarks

Question 16

What are isotopes?

Answer 16

Isotopes are atoms of the same element with different numbers of neutrons and different masses
However, they have the same number of protons and electrons

Question 17

The current model of the atom

Answer 17

Protons and neutrons are found in the nucleus, which is at the centre of the atom
Electrons orbit the nucleus in shells
The nucleus is tiny compared with the total volume of an atom
Nucleus is however extremely dense and accounts for almost all of the atom’s mass
Most of an atom consists of empty space between the tiny nucleus and electron shells

Question 18

The proton

Answer 18

Positively charged, 1+

Relative mass of 1

Question 19

The neutron

Answer 19

No charge

Relative mass of 1

Question 20

The electron

Answer 20

Negatively charged, 1-

Relative mass of 1/2000

Question 21

Reactions of isotopes

Answer 21

Different isotopes of the same element react in the same way
This is because…
Isotopes have the same number and arrangement of electrons
Neutrons make no difference to chemical reactivity

Question 22

Why are ions charged?

Answer 22

Ions are charged because they have unbalanced numbers of protons and electrons, therefore the charges no longer cancel each other out

Question 23

What is relative isotopic mass?

Answer 23

The mass of an atom of an isotope compared with 1/12th mass of an atom of carbon-12

Question 24

What is relative atomic mass?

Answer 24

The weighted mean mass of an atom of an element compared with 1/12th mass of an atom of carbon-12

Question 25

What is the unit that measures atomic masses?

Answer 25

The unified atomic mass unit, u

1 u is a tiny mass
The mass of carbon-12 is defined as 12 u
Therefore, the mass of 1/12 of a carbon-12 atom is 1 u

Question 26

Relationship between relative isotopic mass and the mass number

Answer 26

Both are the same

Eg, oxygen-16 has a relative isotopic mass of 16.0

Question 27

What assumptions have been made regarding the relative isotopic mass and the mass number?

Answer 27

The tiny contribution that electrons make to the mass of an atom
The masses of both a proton and a neutron as 1.0u