atomic physics - atomic structure

Question 1

what is the nucleus of an atom made up of

Answer 1

positively charged protons
no charge neutrons

Question 2

what do electrons do

Answer 2

they are negatively charged particles that orbit the nucleus some distance away

Question 3

what is a neutrally charged atom (in terms of protons, electrons, and neutrons)

Answer 3

a neutrally charged atom has:
equal number of protons and electrons (so charge is balanced)
number of neutrons may vary

Question 4

what is an isotope

Answer 4

an isotope of an element are atoms that have the same number of protons (they determine the element) but different number of neutrons (so the mass number is different)

Question 5

what are ions

Answer 5

ions are charged particles that form when atoms gain or lose electrons

ion with a negative charge - gained extra electrons

ion with a positive charge -
lost electrons

Question 6

explain the:
atomic number
mass number
of an atom

Answer 6

atomic number - the number of protons (same as electrons) in a neutral atom

mass number - the number of neutrons added to the number of protons in a neutral atom

Question 7

the plum pudding model

Answer 7

until early 20th century, scientists believed JJ THOMPSON’S idea that an atom was:
- made up of a series of negatively charged electrons
- the electrons were surrounded by positively charged matter
- the atom had a neutral charge

Question 8

alpha scattering

Answer 8

RUTHERFORD asked Geiger and Marsden to investigate the plum pudding model.

they fired alpha particles at a thin piece of gold foil - after being deflected by the atoms in the foil, the alpha particles would be detected on a screen

if the plum pudding model was true:
- alpha particles would pass through the gold atoms almost unaffected (cos of the evenly distributed positive and negative charge)

HOWEVER:
- most A particles went through unaffected but some got deflected back
- something was interfering with the A particles

1/8000 had a large deflection and 0.14 had a small deflection showing that there is a small, positively charged nucleus

by 1932 - RUTHERFORD and CHADWICK discovered the nucleus was made of positively charged protons and neutrally charged neutrons

Question 9

the nuclear model

Answer 9

RUTHERFORD concluded that:
- the positive nucleus of the atom must be very small compared to the atom
- the nucleus is positively charged to repel alpha particles
- electrons must therefore be orbiting the nucleus - far enough away so it doesn’t interfere but close enough to maintain a neutral charge
- most of the atom is made of empty space

this led to the discovery of the arrangement of electrons and presence of protons and neutrons