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5.1-The nuclear model of an atom

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IGCSE Physics Notes / The Nuclear Model of an Atom

 

 

Summary Fill in the Blanks + Exam Practice

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1The Atom

An atom contains a positively charged
_______nucleus
with negatively charged
_______electrons
in orbit around it.
Positive ions are formed by
_______losing
electrons.
Negative ions are formed by
_______gaining
electrons.
Alpha-particle scattering showed that the nucleus is very
_______small
compared with the atom.
It also showed that most of the atom is
_______empty space
.
The nucleus contains most of the
_______mass
of the atom.
The nucleus is
_______positively charged
.

2The Nucleus

The nucleus is made of
_______protons
and
_______neutrons
.
The relative charge of a proton is
_______+1
.
The relative charge of a neutron is
_______0
.
The relative charge of an electron is
_______?1
.
The proton number is also called the
_______atomic number
and is represented by
_______Z
.
The nucleon number is also called the
_______mass number
and is represented by
_______A
.
Number of neutrons =
_______nucleon number ? proton number
.
Nuclide notation is written as
_______AZX
.
Isotopes are atoms of the same element with the same number of
_______protons
but different numbers of
_______neutrons
.
An element may have more than one
_______isotope
.
The proton number determines the relative
_______charge
on a nucleus.
The nucleon number determines the relative
_______mass
of a nucleus.

3Nuclear Fission and Fusion

Nuclear fission is the
_______splitting
of a nucleus.
Nuclear fusion is the
_______joining
of nuclei.
In both processes, some mass is converted into
_______energy
.

Exam Practice – Click to Reveal Answers

Describe the structure of an atom.
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An atom has a small positively charged nucleus at the centre.

Negatively charged electrons orbit around the nucleus.

Explain how atoms form positive ions and negative ions.
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A positive ion is formed when an atom loses one or more electrons.

A negative ion is formed when an atom gains one or more electrons.

Describe how alpha-particle scattering supports the nuclear model of the atom.
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Most alpha particles passed straight through the foil, showing that most of the atom is empty space.

A few alpha particles were deflected through large angles, showing that the nucleus is very small and contains most of the mass of the atom.

Because alpha particles are positively charged, the deflection also shows that the nucleus is positively charged.

Define proton number and nucleon number.
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Proton number (atomic number), Z: the number of protons in the nucleus.

Nucleon number (mass number), A: the total number of protons and neutrons in the nucleus.

How do you calculate the number of neutrons in a nucleus?
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Number of neutrons = nucleon number ? proton number.

Explain what is meant by an isotope.
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Isotopes are atoms of the same element.

They have the same number of protons but different numbers of neutrons.

Describe nuclear fission and nuclear fusion.
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Nuclear fission is the splitting of a large nucleus into smaller nuclei.

Nuclear fusion is the joining of small nuclei to form a larger nucleus.

In both processes, some mass is converted into energy.

What is the relationship between proton number and the relative charge on a nucleus?
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The proton number tells you how many protons are in the nucleus.

Since each proton has charge +1, the proton number determines the relative charge of the nucleus.

What is the relationship between nucleon number and the relative mass of a nucleus?
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The nucleon number is the total number of protons and neutrons in the nucleus.

Because protons and neutrons each contribute to the mass, the nucleon number determines the relative mass of the nucleus.

Exam Summary

An atom has a small positively charged nucleus with electrons orbiting around it.

The nucleus contains protons and neutrons.

Proton number = number of protons. Nucleon number = protons + neutrons.

Number of neutrons = nucleon number ? proton number.

Isotopes have the same proton number but different neutron numbers.

Alpha-particle scattering showed that atoms are mostly empty space with a small, massive, positively charged nucleus.

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Syllabus Objectives

IGCSE Physics Notes The nuclear model of an atom

5.1.1 The atom

CORE OBJECTIVES:

  • Describe the structure of an atom in terms of a positively charged nucleus and negatively charged electrons in orbit around the nucleus
  • Know how atoms may form positive ions by losing electrons or form negative ions by gaining electrons

EXTENDED/SUPPLEMENT OBJECTIVES:

  •  Describe how the scattering of alpha  particles by a sheet of thin metal supports the nuclear model of the atom, by providing evidence for:
  • (a) a very small nucleus surrounded by mostly empty space
  • (b) a nucleus containing most of the mass of the atom
  • (c) a nucleus that is positively charged

5.1.2 The nucleus

CORE OBJECTIVES:

  • Describe the composition of the nucleus in terms of protons and neutrons
  • State the relative charges of protons, neutrons and electrons as +1, 0 and –1 respectively
  •  Define the terms proton number (atomic number) Z and nucleon number (mass number) A and be able to calculate the number of neutrons in a nucleus
  •  Use the nuclide notation
  • Explain what is meant by an isotope and state that an element may have more than one isotope

EXTENDED/SUPPLEMENT OBJECTIVES:

  •  Describe the processes of nuclear fission and nuclear fusion as the splitting or joining of nuclei, to include the nuclide equation and qualitative description of mass and energy changes without values
  •  Know the relationship between the proton number and the relative charge on a nucleus 8 Know the relationship between the nucleon number and the relative mass of a nucleus

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