1. Atomic Structure

2. Atomic Size
Atom = Comes from Greek word for “uncuttable” or “indivisible”
Smallest unit of an element that still maintains the properties of that element; Building blocks of matter
Nucleus
Electron Cloud

4. Each “circle” is an individual gold atom

5. - Basic Atomic Parts + Sub-atomic Particles Proton Neutron Electron
Positively charged (+1)
Mass = 1 atomic mass unit (amu)
Found in nucleus of atom
Neutron
Neutrally charged (0)
Mass = 1 amu
Electron
Negatively charged (-1)
Mass ≈ 0 amu (is extremely small)
Found in energy shells outside nucleus of atom + -

6. Basic Atomic Structure
Nucleus
Center of atom
99% of atomic mass in nucleus
Where the protons and neutrons are found
Electron Cloud (Energy Shells)
Regions around nucleus where electrons are found based on how much energy they have
Each shell can only have specific number of electrons
N = 1 shell
Can hold 2 electrons
N = 2 shell
Can hold 8 electrons
N = 3 shell
Can hold 18 electrons
N = 3
N = 2
N = 1
Nucleus

7. _
N = 3 _
N = 2 _ _ _ _
N = 1
Nucleus + _ _ _ + _ _ _ + _ _ _ _ _ _

9. 5 Things to Always Look For
2 electrons (2-)
8 electrons (8-)
Type of Element
Look at chemical symbol
1st letter always capitalized; 2nd letter always lower case
Atomic Number (Z)
It equals the # of protons
Mass Number (A)
(# of protons) + (# of neutrons)
Everything in the nucleus
Charge on Particle
(# of protons) – (# of electrons)
Atom or Ion?
If charge = 0… it is an atom
If charge ≠ 0… it is an ion
2 electrons (2-)
12 protons (12+)
12 neutrons (0) 12 Mg 2+ 24 -

10. Understanding Chemical Symbols
Atomic Number (Z)
Mass Number (A)
Element?
Oxygen
How many protons?
Same as atomic number (Z)
= 8 protons
How many neutrons?
Mass number – atomic number
16 – 8 = 8 neutrons
How many electrons?
Same as atomic number if there are no superscript by letter
If there is a superscript… always do the opposite operation to the atomic number.
If it says 2-, then you ADD 2
If it says 3+, then you SUBTRACT 3
It says 2- here, so you add 2 to the atomic number (8 + 2 = 10 electrons) 8 O 2- 16

11. 6 6 12 14 Changing the Neutrons Has 6 neutrons Has 8 neutrons
ISOTOPES = atoms that are the same element (they have the same number of protons) but they have a different number of neutrons 6 6
Atomic
Number C
Atomic
Number C 12 14
Mass
Number
Mass
Number
protons = 6 neutrons
Has 6 neutrons
protons = 8 neutrons
Has 8 neutrons

12. Important Terms to Know
Element
Substance that cannot be broken down into a smaller substance by chemical means; all atoms have the same number or protons; H or O or Fe or Au
Molecule
2 or more atoms bonded together; H20 or C6H12O6
Ion
A positively or negatively charged atom; the atom has lost or gained an electron
Atomic Number = Z
Number of protons in the nucleus
Mass Number = A
Number of protons + neutrons in the nucleus of an atom
Charge of ion
(Number of protons) – (number of electrons)
Valence electrons
Electron in the outermost shell of the atom; important in bonding

13. O 8 16 Neutral Atom vs. Ion Neutral Atom (Example: Oxygen Atom)
6 electrons (6-)
Neutral Atom (Example: Oxygen Atom)
Has specific number of protons
Oxygen Atom = __8 protons__(ALWAYS)
Number of neutrons is similar to protons
Oxygen Atom = __8 neutrons___
Number of electrons is the same as protons
Oxygen Atom = __8 electrons___
Ion (Example: Oxygen Ion)
Oxygen Ion = _8 protons___(ALWAYS)
Oxygen Ion = __8 neutrons__
Number of electrons is DIFFERENT from protons
Oxygen Ion = __10 electrons__
2 electrons (2-)
8protons (8+)
8neutrons (0) 8 O 16
8 electrons (8-)
2 electrons (2-)
8protons (8+)
8neutrons (0)

14. 16 8 16 2- 8 Atomic Number (Z) 8 protons = 8 Mass Number (A)
8 protons + 8 neutrons = 16 amu
Charge
(8+ protons) + (8- electrons) = 0
8 protons – 8 electrons = 0 O
2 e (2-) 8
8 P (8+)
8 N (0)
Neutral Atom 16
8 e (8-)
Atomic Number (Z)
8 protons = 8
Mass Number (A)
8 protons + 8 neutrons = 16 amu
Charge
(8+ protons) + (10- electrons) = 2-
8 protons – 10 electrons = 2- O
2 e (2-) 2- 8
8 P (8+)
8 N (0)
Ion

15. An atom has a mass number (A) of 35.
Practice Problem #1
An atom has a mass number (A) of 35.
If it has 17 protons, how many neutrons does it have?
35 – 17 = 18 neutrons
What is the atomic number (Z)? 17
What element would it be?
Chlorine
If it has 17 electrons, what would the charge on the atom be?
17 protons – 17 electrons = 0 (it is a neutral atom)

16. An atom has a mass number (A) of 24.
Practice Problem #2
An atom has a mass number (A) of 24.
If it has 12 protons, how many neutrons does it have?
24 – 12 = 12 neutrons
What is the atomic number (Z)? 12
What element would it be?
Magnesium
If it has 10 electrons, what would the charge on the atom be?
12 protons – 10 electrons = 2+ (it is an ion)

17. An atom has a mass number (A) of 14.
Practice Problem #3
An atom has a mass number (A) of 14.
If it has 7 protons, how many neutrons does it have?
14 – 7 = 7 neutrons
What is the atomic number (Z) 7
What element would it be?
Nitrogen
If it has 10 electrons, what would the charge on the atom be?
7 protons – 10 electrons = 3- (it is an ion)

18. Exit Ticket 1. Which statement about the atomic nucleus is correct?
A. The nucleus is made of protons and neutrons and has a negative charge.
B. The nucleus is made of protons and neutrons and has a positive charge.
C. The nucleus is made of electrons and has a positive charge.
D. The nucleus is made of electrons and has a negative charge.

19. 2. The charge of an electron is-1 -2 +1

20. 3. Atoms have no electric charge because they:
have an equal number of charged and noncharged particles.
B. have neutrons in their nuclei.
C. have an equal number of electrons and protons.
D. have an equal number of neutrons and protons.

21. An atom’s mass number equals the number of:
protons plus the number of electrons.
protons
protons plus the number of neutrons.
neutrons.