Page 200 - Science Course 1 (Book 1)

The Atom Mo6-L2a: How do Atoms Differ?
Lesson 2

Mass number
In this topic, you will learn the following
lessons: is the sum of the number of protons and neutrons in
an atom.
Mo.6-L2a: How do Atoms Differ?
Mo.6-L2b: What is a Nuclear Decay? Mass number 4 Element
Atomic 2 He Symbol
Number

Mo6-L2a How do Atoms Differ?
Average atomic mass

is the average mass of the element’s isotopes,
KEY CONCEPTS: weighted according to the abundance of each
1. Hows does a neutral atom change when its number isotope.
of protons or electrons changes?

Name neon
Vocabulary A-Z Average 20.18 Symbol

Let us learn some vocabulary atomic mass
Atomic Ne
number 10
Atomic number ion is an atom that is no longer neutral becase it

is the number of protons in an atom of an element. has gained or lost electrons.

Let’s Begin

The Parts of the Atom

The mass of electrons is much smaller than the
mass of protons or neutrons.

Most of the mass of an atom is found in the nucleus.
Isotope
Properties of Protons, Neutrons,
is atoms of the same element that have different
numbers of neutrons. and Electrons

ELECTRON PROTON NEUTRON
e- e-
n p+
p+

Deuterium Protium Symbol e - p n

Charge 1 - 1 + 0

e- electron nucleus nucleus
n cloud
p+ Location
n around
the nucleus

Relative
Tritium mass 1 / 1, 840 1 1
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