Download Section 3.2 Day 2

Friday, Oct. 25th: “A” Day
Monday, Oct. 28th: “B” Day
Agenda
Finish section 3.2: “Structure of Atoms”
Atomic number, mass number, isotope
Movie: “Writing Nuclear Symbols” and worksheet
Homework:
Sec. 3.2 review, pg. 89: #1-8
Finish movie worksheet
Concept Review: “Structure of Atoms”
Atomic Number is the Number of
Protons in the Nucleus
Atomic Number: the number of protons in
the nucleus of an atom; the atomic number is
the same for all atoms of an element.
No two elements can have the same atomic
number.
The Atomic Number Also Tells the
Number of Electrons
The atomic number also reveals the number
of electrons in an atom. Why?
For atoms to be electrically neutral, the
number of positively charged protons must
equal the number of negatively charged
electrons.
If you know the number of protons in an
atom, you automatically know the number of
electrons too!
Mass Number is the Number of
Particles in the Nucleus
Mass Number: the sum of the numbers of
protons and neutrons of the nucleus of an
atom. (also called atomic mass)
Protons
+ Neutrons
Mass Number
Unlike the atomic number, the mass number
can vary between atoms of a single element.
Atomic Number/Mass Number
Sample Problem A, pg. 86
How many protons, electrons, and neutrons
are there in an atom of copper whose atomic
number is 29 and whose mass number is 64?
Atomic number = number of protons = 29
Protons = electrons = 29
Mass number = protons + neutrons
64 = 29 + Neutrons
Neutrons = 35
Practice Problem #3, pg. 86
Calculate the mass number for an atom that
has 45 neutrons and 35 electrons.
Mass number = protons + neutrons
Protons = electrons = 35
Mass number = 35 + 45
Mass number = 80
Which element is this?
Bromine (Br)
Atomic Structures Can Be Represented
by Symbols (nuclear symbols)
Each element has a name and symbol that is
listed in the periodic table of elements.
Sometimes, atomic numbers and mass
numbers are written with an element’s
symbol.
Atomic #: whole number
Mass #: has decimal point
Atomic Structures Can Be Represented
by Symbols
The atomic number always appears on the lower
left side of the element’s symbol:
1H
2He
3Li
4Be
5B
Mass numbers are written on the upper left side
of the symbol:
1
1H
2
4He
3
7Li
4
9Be
5
11B
**mass number = protons + neutrons**
Isotopes of an Element Have the Same
Atomic Number
All atoms of an element have the same atomic
number and the same number of protons.
However, atoms of the same element do not
necessarily have the same number of neutrons.
Isotope: an atom that has the same number of
protons (atomic number) as other atoms of the
same element, but has a different number of
neutrons (atomic mass).
Two Ways of Identifying Isotopes
1. Write the mass number with a hyphen after the
symbol for the element:
He-3
 This is a helium atom with a mass number of 3.
2. Write the nuclear symbol for the isotope:
3He
2
 This is also a helium atom with a mass number
of 3.
*Remember: all isotopes of an element have
the same atomic number and the same
number of protons!*
Sample Problem B, pg. 89
 Calculate the number of protons, electrons, and
neutrons in oxygen-17 and in oxygen-18.
 These are both isotopes of oxygen, whose atomic
number is 8.
 Atomic number = number of protons = 8
 Protons = electrons = 8
 Mass number = proton + neutrons
 For oxygen-17: 17 = 8 + neutrons
Neutrons = 9
 For oxygen-18: 18 = 8 + neutrons
Neutrons = 10
Movie: “Writing Nuclear Symbols”
The movie is really short, about 8 minutes.
Worksheet
Complete the front side of the worksheet
that goes along with the movie
The back side is homework
Homework
Section 3.2 review, pg. 89: #1-8
Finish “Writing Nuclear Symbols” worksheet
Concept Review: “Structure of Atoms”
*Be ready for a quiz over section 3.2 next time*