6.4.1 Atoms and isotopes

Question 1

Atoms are very small, having a radius of about?

Answer 1

1 × 10-10 metres

Question 2

The basic structure of an atom is ?

Answer 2

a positively charged nucleus
composed of both protons and neutrons surrounded by negatively
charged electrons

Question 3

The radius of a nucleus is?

Answer 3

less than 1/10 000 of the radius of an
atom.

Question 4

Most of the mass of an atom is ?

Answer 4

concentrated in the nucleus

Question 5

The electrons are arranged at

Answer 5

different distances from the nucleus
(different energy levels).

Question 6

what might the electron arrangements may change with?

Answer 6

the absorption of electromagnetic radiation (move further from
the nucleus; a higher energy level) or by the emission of
electromagnetic radiation (move closer to the nucleus; a lower
energy level)

Question 7

Atoms of the same element can have different numbers of
neutrons;

Answer 7

these atoms are called isotopes of that element.

Question 8

New experimental evidence may lead to?

Answer 8

a scientific model being
changed or replaced.

Question 9

Before the discovery of the electron, what were atoms thought to be?

Answer 9

tiny
spheres that could not be divided.

Question 10

The discovery of the electron led to ?

Answer 10

the plum pudding model of the
atom

Question 11

what does the plum pudding model suggest?

Answer 11

that the atom is a ball of
positive charge with negative electrons embedded in it.

Question 12

The results from the alpha particle scattering experiment led to the
conclusion that?

Answer 12

the mass of an atom was concentrated at the centre
(nucleus) and that the nucleus was charged. This nuclear model replaced the pum pudding model

Question 13

Niels Bohr adapted the nuclear model by suggesting?

Answer 13

that electrons
orbit the nucleus at specific distances. The theoretical calculations
of Bohr agreed with experimental observations

Question 14

Later experiments led to the idea that?

Answer 14

the positive charge of any
nucleus could be subdivided into a whole number of smaller
particles, each particle having the same amount of positive charge.
The name proton was given to these particles.

Question 15

The experimental work of James Chadwick provided the evidence
to show the existence of?

Answer 15

neutrons within the nucleus –>about 20 years after the nucleus became an accepted scientific
idea.