Download Atomic Structure

2/19/16 Do Now

On your half sheet of paper, identify the
scientist that either discovered a part of
the atom or developed a theory related
to atomic structure.
Vocabulary Review
Atom
 Cathode Ray
 Electrons
 Protons
 Neutrons
 Nucleus


How many protons, electrons, and neutrons
are in the element Tin (Sn)?

By the end of today, you will know how to
find the answer
Atomic Structure
Protons, Neutrons, and Electrons
SLO 2/19/16
Students will be able to interpret how
elements are different from each other and
how atomic mass and atomic numbers are
determined.
4.3
Distinguishing Among Atoms

Just as apples come
in different varieties,
a chemical element
can come in
different “varieties”
called isotopes.
Protons

Protons- determine the identity of an
atom
◦ Elements are different because they each have
different #s of protons

The atomic number of an element is
the number of protons in the nucleus of
an atom of that element
◦ You can find this number by looking at your
periodic table

In a neutral atom, the number of protons
is equal to the number of electrons
Atomic Number
Practice Finding # of protons and
electrons
Finding the number of Neutrons

The total number of protons and neutrons
in an atom is called the mass number.
◦ The number of neutrons in an atom is the
difference between the mass number and atomic
number.
◦ How do I find the mass number?
 If given, add the protons and neutrons together
 If not, round the mass from the periodic table to the
nearest whole number. This will provide the mass
number of the most common isotope.
Finding Protons, Neutrons,
Electrons

You may be given only the name of an
element and be expected to look it up on
the periodic table.

You may be given a symbol with mass
numbers and atomic numbers beside it.
Writing and Interpreting Chemical
Symbols
Mass of an atom

Nucleus- contains most of the mass of
an atom
◦ Protons & Neutrons contain most of an
atom’s mass
 Mass of proton = mass of neutron = 1amu
◦ Electrons- 1/2000th of the mass of a proton
Atomic structure

Grams are not used to measure mass
of atoms because atoms are too small
◦ Amu is used instead
◦ Amu = atomic mass unit

Amu – 1/12th the mass of a carbon-12
atom, which contains 6 protons and 6
neutrons
Isotopes

Isotopes are atoms that have the same number
of protons but different numbers of neutrons.
◦ Because isotopes of an element have different
numbers of neutrons, they also have different
mass numbers.
4.3
Isotopes
 Despite these differences, isotopes are chemically
alike because they have identical numbers of
protons and electrons.
Isotopes

To indicate the identity of an isotope, write the
element name – mass #
◦ Carbon-12 Carbon-14
◦ Isotopes can also be indicated using the method we
saw earlier
Independent Practice

Work on the Protons, Neutrons, and
Electrons of Elements worksheet. This will
count as a classwork grade when finished.
Element
Symbol
Protons
Electrons
Neutrons
Hydrogen
H
1
1
0
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium
Beryllium
Magnesium
Calcium
Strontium
Barium
Radium
For the Quiz…

Define and indicate location of:
◦ Proton
◦ Neutron
◦ Electron

Explain:
◦ Dalton’s Theory
◦ Thomson’s Theory
◦ Rutherford’s Theory

Dalton
All elements are composed of tiny indivisible particles called atoms.
Atoms of the same element are identical. The atoms of any one element are
different from those of any other element.
Atoms of different elements can chemically combine in simple whole-number
ratios to form compounds.
Atoms of one element are never changed into atoms of another element in a
chemical reaction.
1)
2)
3)
4)

Thomson
◦ Plum Pudding Model
◦ Atoms have positive and negative charges
◦ Discovered the Electron

Rutherford
◦
◦
◦
◦
Gold Foil Experiment
Alpha particles projected toward gold foil
Atoms mostly empty space
Nucleus- region of high mass and positive charge
Plum Pudding Model
Finish the chart:
Element
Symbol
Hydrogen
H
Lithium
Magnesium
1
23 (22.99)
39 (39.09)
Cs
Protons Electrons Neutrons
3
37
Fr
Beryllium
11
K
Rubidium
Cesium
Mass
Number
1
3
Na
Potassium
Atomic
Number
19
87
87
9 (9.01)
12
4
11
12
19
37
133 (132.91)
Be
3
24 (24.30)
38
55
78
87
136
4
12
12
Homework

Reading Assignment: Section 4.3

Written Assignment: Complete the Atomic
Identifiers Worksheet

Quiz Wed (11/20/13) on Atomic Theory and
Structure. Chapter 4, Sections 1 & 2

Complete Pre-Lab for “Mass of Candium” Lab
found on page 120 of the textbook.
Lab will be on Friday, November 22nd.

2/22/16 Do Now
Homework Check!
Vocabulary Review
Mass number
 Atom
 Isotope
 Cathode Ray
 Electrons
 Atomic number
 Protons
 Neutrons
 Nucleus

Quiz Time!

You have 35 minutes to complete the
quiz.
11/14/14 SLO
Students will be able to calculate the average atomic
mass of elements and isotopes.
Homework!
Complete Pre-Lab for “Mass of Candium”
Lab found on page 120 of the textbook.
 Lab will be on Friday, November 22nd.

Calculating the Average atomic mass
of an element

Average atomic mass- a weighted average
of the masses of the isotopes of an
element
Average atomic mass = (% x mass) + (% x mass) + (% x mass)….
Example of average atomic mass for carbon
mass number
13
exact weight
percent
abundance
12
12.0000 amu
98.90
13
13.003355 amu 1.10
(12.0000amu) (0.9890) + (13.003355amu) (0.0110) = 12.011 amu
Check your answers
C has an average atomic mass of
12.011 amu.
 This is closer to 12 than to 13, which
means most isotopes must be
carbon-12.
 This matches our known data, which
say that 98.90% of carbon atoms are
C-12.

Isotopes and Weighted Averages

Ways to write isotopes:
◦ Carbon-14
◦ 14C
14
◦ 6C
Isotopes and Weighted Averages
Nitrogen has two isotopes; Nitrogen-14 with a
99.634% abundance and Nitrogen- 15 with a
0.366% abundance. Calculate the Average
Atomic Mass.
Step 1: Write out the mass number and %
abundance as a multiplication problem with a
decimal
14N = 99.634% (14)x(.99634) =
15N = 0.366%
(15)x(.00366) =
Isotopes and Weighted Averages
Nitrogen has two isotopes; Nitrogen-14 with a
99.634% abundance and Nitrogen- 15 with a
0.366% abundance. Calculate the Average
Atomic Mass.
Step 2: Do your math and multiply.
14N
= 99.634% (14)x(.99634) = 13.94876
15N = 0.366%
(15)x(.00366) = 0.0549
Isotopes and Weighted Averages
Nitrogen has two isotopes; Nitrogen-14 with a
99.634% abundance and Nitrogen- 15 with a
0.366% abundance. Calculate the Average
Atomic Mass.
Step 3: Add the products together to get the
average atomic mass of the element.
14N
= 99.534% (14)x(.99534) = 13.94876
15N
= 0.366%
(15)x(.00366) = 0.0549
14.00366
+
Isotopes and Weighted Averages
Try these:
Find the average atomic mass of Potassium
given the isotopes and relative
abundances:
Potassium -39 (93.26%)
Potassium -40 (0.012%)
Potassium -41 (6.73%)
Isotopes and Weighted Averages
Try these:
Find the average atomic mass of Molybdenum
given the isotopes and relative abundances:
92Mo
14.84%
94Mo 9.25%
95Mo 15.92%
96Mo 16.68%
97Mo 9.55%
98Mo 24.13%
100Mo 9.63%
Throughout this section, we’ve been
using the periodic table

A periodic table is an arrangement of
elements in which the elements are
separated into groups based on a set of
repeating properties.
◦ A periodic table allows you to easily compare
the properties of one element (or a group of
elements) to another element (or group of
elements).
Periodic Table

Each horizontal row of the periodic table
is called a period.

Within a given period, the properties of
the elements vary as you move across it
from element to element.
◦ This occurs because they have a different
number of outer shell (or valence) electrons
4.3
The Periodic Table—A Preview
 A Period
Periodic Table

Each vertical column of the periodic table
is called a group, or family.

Elements within a group have similar
chemical and physical properties.
◦ This occurs because they have the same
number of valence (or outer shell) electrons
4.3
The Periodic Table—A Preview
 A Group or Family
Homework!
Complete Pre-Lab for “Mass of Candium”
Lab found on page 120 of the textbook.
 Lab will be on Friday, November 22nd.
