Download Atom Basics

Atom Basics
The Subatomic Particles
Protons (p+) :
 Have +1 Charge
 Have a mass of 1 amu (atomic mass unit)
Electrons (e-):
 Have a -1 charge
 Have a mass of 0.0005 amu
Neutrons (n0):
 Have no charge
 Have a mass of 1 amu
Atomic Structure
Electron Cloud Model

Nucleus


Incredibly small
Contains all the protons
and neutrons
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
Nucleus is very dense
Rest of the atom

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Mostly empty space
The electrons move around
in the empty space
No Specific Orbits

Use a cloud to show the
probability of finding an
electron = orbital
How do we describe atoms?

Every element has its
own atomic number

Atomic number is on
top in the blocks in
the periodic table
Atomic Number = Z =
number of protons

How do Protons and Electrons
Relate?

If an atom has no charge then…

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The number of electrons must equal the
number of protons.
If the atom has a charge then its called an
ion
Positively charged ions = cations
 Negatively charged ions = anions

How do Protons and Electrons
Relate?

How do atoms become charged?

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Only the number of electrons changes

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Protons are buried deep in the nucleus and so
they don’t change.
Positive charge

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Comes from imbalance in protons and
electrons
Lost electrons
Negative charge

Gained electrons
What about neutrons?

Imagine three atoms:
Atom 1: 6 protons, 6 electrons, 6 neutrons
 Atom 2: 6 protons, 6 electrons, 7 neutrons
 Atom 3: 6 protons, 6 electrons, 8 neutrons

What element are they?
 All the same element but the atoms aren’t
the same
 Isotopes – Atoms with the same number of
protons but different numbers of neutrons

How do we tell the atoms apart?
Atom 1: 6 protons, 6 electrons, 6 neutrons
 Atom 2: 6 protons, 6 electrons, 7 neutrons
 Atom 3: 6 protons, 6 electrons, 8 neutrons


Mass Number = protons + neutrons


Symbol = A
Not every isotope is represented evenly.
How do we adjust for different
isotopes?


Average atomic mass –
weighted average of
the masses of all the
isotopes.
Bottom number on
Periodic Table
Average Atomic Mass

Carbon has two naturally occurring
isotopes:
Carbon with a mass number of 12 – 98.93%
 Carbon with a mass number of 13 – 1.07%


(12 amu * 0.9893) + (13 amu * 0.0107) =
12.0107 amu
What is the shorthand?



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X = symbol of the
element
A = mass number
Z = atomic number
Q = charge (left off if
not charged)
Also see just X–A
C-13
A
Z
X
13
6
Q
C
Practice
49
22
Ti
4

What is the atomic number?

What is the atomic mass?

What is the mass number?

How many protons?

How many neutrons?

How many electrons?