Download atomic number

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Chapter 2-1 Study Guide
Atoms
Ms. Grady
What is matter?
 Matter is anything that has mass and takes up space.
***Mass is the amount of matter in an object.
 Matter is made up of tiny particles called atoms.
 There are over 90 types of atoms having different sizes.
Examples of Matter Examples of what is not matter
 Liquids
 Heat
 Rocks
 Light
 A body
 ideas
 The structure (composition) of different types of atoms and
how they are joined together determine its properties.
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Elements
Most other objects that you see are made of several different
types of atoms
Some substances are made of only 1 type of atom.
Elements = substances that are made of only 1 type of atom and
cannot be broken down into simpler substances by normal
chemical or physical means.
Minerals usually are combinations of atoms that occur in nature
as solid crystals and are usually found as mixtures in ores.
Some minerals are only made up of only 1 element.
These minerals, which include copper and silver are called native
elements.
Copper
copper wire
silver
silverware
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Modeling the Atom
 When something is too large or too small to observe directly,
models can be used.
 Ex. Model airplane or a model of an atom
 A model is a small version of a larger object.
The History of the Atomic Model
 More than 2,300 years ago, the Greek philosopher, Democritus,
proposed that matter is composed of small particles called
atoms.
 More than 2,000 years later, John Dalton expanded on these
ideas.
 He theorized that all atoms of an element contain the same
type of atom.
Protons and Neutrons
3 basic particles make up an atom
 protons
 neutrons
 electrons
Protons are particles that have a positive (+) electric charge.
Neutrons have no electric charge.
Both particles are located in the nucleus – the center of an atom.
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With no negative charge (-) to balance the positive charge (+) of the
protons, the charge of the nucleus is positive (+).
How many particles are in an atom? 3
Particles
Charge
Location
1.Protons
(+) positive
In the nucleus
2.Neutrons
(0) neutral
In the nucleus
3.Electrons
(-) negative
Outside the nucleus
Electrons
Particles of a negative charge are called electrons.
 Electrons exist outside of the nucleus.
1913 – Niels Bohr, a Danish scientist, proposed that an atom’s
electrons travel in orbit like paths around the nucleus.
He also proposed that electrons in an atom have energy that
depends on their distance from the nucleus.
The Current Atomic Model
Over the next several decades, research showed that electrons can
be groups into energy levels, each holding only a specific number of
electrons.
Electrons do not travel in orbit like paths.
Scientists use a model that resembles a cloud surrounding a nucleus.
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Counting Atomic Particles
The number of protons in an atom depends on the element.
All atoms have the same number of protons.
 For example, all iron atoms contain 26 protons, and all atoms with
26 protons are iron atoms.
The number of protons in an atom is = to the atomic number of the
element.
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What is the atomic number of Helium (He)? Answer: 2
What is the atomic number of Silver (AG)? Answer 4
How many Electrons?
In a neutral atom, the number of protons is = to the number of
electrons.
This makes the overall charge of the atom = zero (0).
Atomic number = number of protons= number of electrons
Atoms of an element can lose or gain electrons and still be the same
element.
When this happens, the atom is no longer neutral.
Atoms with fewer electrons than protons have a positive (+) charge.
Atoms with more electrons than protons have a negative (-) charge.
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How many Neutrons?
Atoms of the same element can have different numbers of neutrons
(not like protons).
 The number of neutrons in an atom is not found on the periodic
table. You need to be given the atom’s mass number.
The mass number of an atom is = to the number of protons + the
number of neutrons.
The number of neutrons is determined by subtracting the atomic
number from the mass number.
 Ex. Mass number of nitrogen = 14 and the atomic number = 7
Isotopes = Atoms of the same element that have different numbers
of neutrons.
What is the number of neutrons in Carbon- 12?
We know that 12 is the mass number. We also know the atomic number is 6.
Therefore, 12- 6 = 6. The number of neutrons in Carbon-12 is 6.
Example of Isotopes of Hydrogen and Carbon
Isotope
Number
Number
Number
Atomic
of
of
of
Number
Protons
Neutrons Electrons
Hydrogen - 1
1
0
1
1
Hydrogen - 2
1
1
1
1
Hydrogen - 3
1
2
1
1
Carbon -12
6
6
6
6
Carbon - 14
6
8
6
6
Mass
Number
1
2
3
12
14
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