1) Atoms are the smallest particle of an element that retains the properties of that element. 2) Atoms consist of electrons that orbit a nucleus, which contains protons and neutrons. 3) Protons have a positive charge, electrons have a negative charge, and neutrons have no charge. The number of protons defines the element. 4) Atoms are electrically neutral when they contain an equal number of protons and electrons. Ions are formed when atoms gain or lose electrons.

1. INSIDE THE ATOM

2. INSIDE THE ATOM
RECALL: Elements and Compounds
ELEMENT COMPOUNDS
A substance that can not be 2 or more elements that
broken down by chemical or are chemically joined
physical means
Sodium Bromine Oxygen table salt ethanol carbon dioxide
(NaCl) (C2H5OH) (CO2)
(Na) (Br2) (O2)
Elements cannot be broken down into simpler substances by ordinary
chemical means (burning, electricity, or chemical reactions)

3. INSIDE THE ATOM
There are 112+ different elements in the universe
(e.g. gold, oxygen, lead, iron)

4. INSIDE THE ATOM
The smallest piece of an element that is still the
element is called an atom

5. INSIDE THE ATOM
Inside an atom:
Electrons
Nucleus

6. INSIDE THE ATOM
Inside an atom:
Electrons: Negatively-charged particles that orbit around the
nucleus in fixed levels.
= -1
= -1
= -1
-Each electron has a charge of -1
-Electrons are so small and light that they are said to have almost
no mass.

7. INSIDE THE ATOM
Inside an atom:
What attracts the electrons to the nucleus?
(HINT: What attracts a negative charge?)
= -1
= -1
= -1

8. INSIDE THE ATOM
Inside an atom:
Nucleus: The centre of the atom, which is made of protons and
neutrons.
proton neutron

9. INSIDE THE ATOM
Inside the nucleus:
Proton: Positively charged particle, with a mass of 1 u
= +1
Neutron: Neutral particle, with a mass of 1 u
=0
u = atomic mass unit = 1.660538921×10−27 kg

10. INSIDE THE ATOM
Summary:
Diagram Mass Charge
Electron 0u -1
(outside nucleus)
Proton 1u +1
(inside nucleus)
Neutron 1u 0
(inside nucleus)

11. INSIDE THE ATOM
In a neutral atom,
Number of protons = number of electrons
+5 -5
There is no overall charge

12. INSIDE THE ATOM
What if the number of protons and electrons did not match?
Number of protons ≠ number of electrons
+5 -4
The overall charge is +1. The atom is charged.
A charged atom is called an ion. An atom becomes
charged when it gains or loses electrons

13. INSIDE THE ATOM
Here is a more accurate, to-scale representation of an atom:
Nucleus
Electrons form a
“cloud” around
the nucleus
An atom is VERY small.

14. INSIDE THE ATOM
How the Periodic Table identifies atoms
11
Na
sodium
22.99

15. INSIDE THE ATOM
How the Periodic Table identifies atoms
atomic number
11
-number of protons
-unique to each atom
-number of electrons in
neutral atom
element symbol
Na
-derived from Latin name
-unique to each atom
element name
sodium
atomic mass
-average atomic mass (u)
-related to number of protons 22.99
and neutrons

16. INSIDE THE ATOM
How the Periodic Table identifies atoms
element symbol
A symbol uses one or two
11
letters (the 1st letter is
always capitalized)
Oxygen (O)
Sodium (Na)
Na
sodium
22.99

17. INSIDE THE ATOM
How the Periodic Table identifies atoms
atomic number -number of protons
-unique to each atom
-number of electrons in neutral atom
11
Na
sodium
22.99

18. INSIDE THE ATOM
How the Periodic Table identifies atoms
atomic mass -average atomic mass
-related to number of protons and neutrons
11
Na
sodium
22.99
22.99 – 11 protons = 12
neutrons

19. INSIDE THE ATOM
How the Periodic Table identifies atoms
Thus the average atomic mass can provide
information regarding the total number of protons
and neutrons
11
Na
sodium
22.99

20. INSIDE THE ATOM
How to represent an element in Standard Atomic Notation:
Mass number (A) = total number of protons and neutrons
Atomic number (Z) = total number of protons
Mass number (A)
23
11
Na
Atomic number (Z)
Both are always whole numbers

21. INSIDE THE ATOM
Identify the atom. Is this an ion?
Number of protons = 7
Number of electrons = 7
.: this is nitrogen, and
is not an ion
N

22. INSIDE THE ATOM
Identify the atom. Is this an ion?
proton
Number of protons = 6
Number of electrons = 8
.: this is carbon (C), and is an
ion (with a -2 charge)
C2-

23. INSIDE THE ATOM
Identify the atom. Is this an ion?
proton
Number of protons = 6
Number of electrons = 6
.: this is carbon (C), and is
not an ion
C

24. INSIDE THE ATOM
Identify the atom. Is this an ion?
proton
Number of protons = 3
Number of electrons = 3
.: this is lithium (Li), and is
not an ion
Li

25. INSIDE THE ATOM
2 or more combined elements will be called a
compound. This is another example of a pure
substance.
ELEMENT COMPOUNDS
A substance that can not be 2 or more elements that
broken down by chemical or are chemically joined
physical means
Sodium Bromine Oxygen table salt ethanol carbon dioxide
(NaCl) (C2H5OH) (CO2)
(Na) (Br2) (O2)