Download What do you already know about atoms?

What do you already know about
atoms?
• Brainstorm about what you already know (or
are pretty sure of…) about atoms.
• Write it down on your paper, then we’ll
discuss.
What are they made of???
• Protons- Positively charged particles located in
the nucleus
• Neutrons- Uncharged particles located inside
the nucleus
• Electrons- Negatively charged particles located
outside the nucleus
Comparing subatomic particles…
relative
mass
(amu)
1/1840
particle
symbol
electron
e
proton
p+
1
neutron
n
0
1
-
History of Atomic Models
• Democritus (~400BC)
– atomos = small, solid, indestructible
particles of different shapes & sizes
– These were just ideas, not truly science…
• Dalton’s Atomic Theory
– Billiard Ball Model - small solid sphere
– Developed notion of conservation of mass
and that atoms combine in specific ratios
History of Atomic Models
• J.J. Thomson
– Plum Pudding Model - positive and
negative particles dispersed
throughout the atom
– Used Cathode Ray tubes to discover
the electron - first subatomic particle
discovered!
https://www.youtube.com/watch?v=XU8nMKkzbT8
Cathode Ray Tube
• A tube that contains a stream of electrons
going from a negative disk (cathode) to a
positive disk.
• Deflected stream showed that electrons are
negative.
Rutherford
– Nuclear Model
– Discovered dense positively charged nucleus of
the atom while working with alpha particles
• Gold Foil Experiment
• http://www.youtube.com/watch?v=XBqHkraf8iE
History of Atomic Models
• Neils Bohr – Also Solar System Model
– Electrons travel in specific, circular orbits
• Schrodinger & Heisenburg – Quantum Mechanical Model
– Dense nucleus w/ protons & neutrons
– Electrons exist in ‘clouds’ called orbitals w/ specific
energy levels
– Mathematical predictions for probability of finding
electrons
– Electrons have particle and wave properties
Do Now
• List the three subatomic particles, their
charges, and where they are located
The Periodic Table
Elements are
so periodic !
“Repeats at regular intervals”
Dimitri Mendeleev
• Russian chemist
• Published first version of
periodic table in 1869
• Put elements in order of
increasing atomic mass
• All elements were not known at
that time, but he was able to
predict the elements that fit in
the gaps.
Atomic Mass
Total of protons and neutrons
found in the nucleus of an atom
Henry Moseley
Early 20th century
improved the table by
arranging the elements ,
by atomic
Number (#protons)
This made it more clear
Which elements were
missing
Atomic Number
Number of protons found in a
nucleus, defines an atom
Modern Periodic table arranged into
periods 1-7
• Horizontal rows of elements
– Side to side
• Increase in Atomic number from left to right
Li
Be
B
C
N
O
F
Ne
Families of Elements
• Vertical columns
of elements
– Up & Down
• Also referred to
as Groups
• Share common
characteristics or
properties
He
Ne
Ar
Kr
Xe
Rn
How to read it
Atomic
Number
Represents the
number of
protons
in the nucleus
Atomic
Mass
Represents the
number of
protons and neutrons
in the nucleus
6
C
12
2
4
Electron
Configuration
Represents
the arrangement
of electrons in
the energy levels
of a Bohr model
Symbol
Represents
the name
of the chemical
Do Now
• Take out your homework…..
Metals
• Similar in many properties
– Luster/Shiny
– Malleable (can be pressed into
sheets)
– Conduct heat and electricity
– Ductile (can be drawn out into
wires)
Nonmetals
– Usually gases or brittle solids
– Most are poor conductors of
heat and electricity
– Most are gases at room
temperature
Metalloids
• Have some properties of both metals
and nonmetals
• Along the stair step
• Ex: boron has luster but is a
• Poor conductor of electricity
Green – metals
Yellow – nonmetals
Blue - metalloids
Do Now
• Use your NEW periodic tables to find the
following information for Oxygen
• Atomic Number
• Atomic Mass
• Number of Protons
• Number of Electrons
• Number of Neutrons
Structure of an atom:
• Nucleus:
–Protons +
–Neutrons 0
• Electrons -
Electrons
• Some electrons are closer to the nucleus than
others.
• The closer to the nucleus the greater the
attraction, therefore the harder to remove.
Bohr Diagram
• The Bohr model, introduced by Niels Bohr in
1913,
• Depicts the atom as a small, positively charged
nucleus surrounded by electrons that travel in
circular orbits around the nucleus
• Similar in structure to the solar system, but
with electrostatic forces providing attraction,
rather than gravity
Electron Energy Stairwell
• Nucleus is the ground floor.
• Electrons closest to the nucleus are the first
floor, they are held most tightly.
• The next sphere is the second floor and so on.
• The first level is also the smallest it can hold 2
electrons.
• Second floor is larger and can hold 8 electrons
• Third floor can hold 18 electrons
• Fourth floor can hold 32 electrons
Hydrogen
1H
Your Bohr
Atomic Mass = 1
- Atomic # = 1
# neutrons = 0
1
Atomic # = # protons = 1
# protons = 1
# neutrons = 0
# electrons = # protons = 1
1
NOTE: There are no
neutrons in a
Hydrogen atom!
Helium
4He
Your Bohr
Atomic Mass = 4
- Atomic # = 2
# neutrons = 2
2
Atomic # = # protons = 2
# protons = 2
# neutrons = 2
2
NOTE: The first level
of Helium is full!
# electrons = # protons = 2
Lithium
7Li
Your Bohr
Atomic Mass = 7
Atomic # = 3
# neutrons = 4
3
Atomic # = # protons = 3
# protons = 3
# neutrons = 4
# electrons = # protons = 3
2
1
NOTE: The first energy
level is full, so the
3rd electron goes to the
next energy level!
Beryllium
9Be
Your Bohr
Atomic Mass = 9
- Atomic # = 4
# neutrons = 5
4
Atomic # = # protons = 4
# protons = 4
# neutrons = 5
# electrons = # protons = 4
2
2
NOTE: There are 2 electrons
on the outer energy level!
Boron
11B
Your Bohr
Atomic Mass = 11
- Atomic # = 5
# neutrons = 6
5
Atomic # = # protons = 5
# protons = 5
# neutrons = 6
# electrons = # protons = 5
2
3
NOTE: There are
3 electrons on the
outer energy level!
Magnesium
24Mg
Your Bohr
Atomic Mass = 24
- Atomic # = 12
# neutrons = 12
12
Atomic # = # protons = 12
# protons = 12
# neutrons =12
2
8
2
NOTE: The outer
level has 2 electrons!
# electrons = # protons = 12
Aluminum
27Al
Your Bohr
Atomic Mass = 27
- Atomic # = 13
# neutrons = 14
13
Atomic # = # protons = 13
# protons = 13
# neutrons =14
# electrons = # protons = 13
2
8
3
NOTE: There are
3 electrons in the
outer energy level!
Silicon
28Si
Your Bohr
Atomic Mass = 28
- Atomic # = 14
# neutrons = 14
14
Atomic # = # protons = 14
# protons = 14
# neutrons =14
# electrons = # protons = 14
2
8
4
NOTE: There are
4 electrons in the
outer energy level!
Phosphorous
Your Bohr
Atomic Mass = 31
- Atomic # = 15
31P
15
# neutrons = 16
Atomic # = # protons = 15
# protons = 15
# neutrons =16
# electrons = # protons = 15
2
8
5
NOTE: There are
5 electrons in the
outer energy level!
Sulfur
Your Bohr
Atomic Mass = 32
- Atomic # = 16
32S
16
# neutrons = 16
Atomic # = # protons = 16
# protons = 16
# neutrons =16
# electrons = # protons = 16
2
8
6
NOTE: There are
6 electrons in the
outer energy level!
Chlorine
35Cl
Your Bohr
Atomic Mass = 35
- Atomic # = 17
# neutrons = 18
17
Atomic # = # protons = 17
# protons = 17
# neutrons =18
# electrons = # protons = 17
2
8
7
NOTE: There is room for only
one more electron in the
outer energy level!
Argon
Your Bohr
Atomic Mass = 40
- Atomic # = 18
40Ar
18
# neutrons = 22
Atomic # = # protons = 18
# protons = 18
# neutrons = 22
2
8
8
NOTE: All three energy
levels are full!
# electrons = # protons = 18
Welcome Back!!!
Do Now
Group
Period
2
4
17
5
13
4
6
6
Element
Name
Element
Symbol
P (+)
N (0)
E (-)
Chemical Activity
• Since the electrons on the inner shells are
buried they cannot leave the atom.
• Which would be the only electrons that can
detach from the atom?
• The one in the last layer!
• They are also the most loosely attached to the
nucleus because they are so far away.
Valence Electrons: The electrons in the
outer most energy level
• To determine the valence electron number look at
the periodic table.
Group #
# Valence electrons
1
1
2
2
3-12
Usually 2
13
3
14
4
15
5
16
6
17
7
18
8* (He 2)
… or look at the box on the periodic
table
Electron
Configuration
6
C
12
2
4
Valence
electrons are
the last number
Dot Diagrams
• Dot diagrams are used to show the number of
valence electrons.
• Carbon = 4 valence electrons
C
• Practice: Write the electron dot diagrams for the following
elements.
• Magnesium
Oxygen
• Nitrogen
Cesium
• Tin
Argon
• Aluminum
Helium
Do Now
•
•
•
•
•
•
•
Take out your homework to be checked
Draw Dot Diagrams of the following elements:
He
Hg
Ar
Pb
P
Fe
O
W
N
I
Chemical Bonding
• All chemical reactions involve the movement
of valence electrons forming or breaking
chemical bonds to form a Compound.
• Compound: Molecule made of two or more
elements.
Magic Number
• The Magic Number- 8(or 0) valence electronsatoms bond to get a full valence shell.
• The last shell wants to be full to be stable!
How can chlorine get another
Electron to become stable?
Ionic Bonds
• Ionic Bonds- forms between a metal and a
nonmetal. Electrons are moved from one
atom to the other.
What happens if valence
electrons are transferred?
• Electrons are exchanged between
objects, giving them a charge.
Metals
•
•
•
•
•
Metals have 1,2 or 3 valence electrons.
Will they give or get electrons?
GIVE!
It’s easier to give away a few than to get a lot.
If metals give away electrons will they become
positive or negative?
•+ positive
Non Metals
•
•
•
•
Nonmetals have 5 or more electrons.
Will they give away or take electrons?
TAKE
It’s easier for them to take a few than to give
away a lot.
• Will they become positive or negative?
•- negative
IONS
• Ion- electrically charged atom formed when
electrons move during reactions
• + ion- Cation formed when electrons are lost
• – ion- Anion formed when electrons are
gained
DO NOW
• What is an ion?
• An electrically charged atom formed when
electrons move during reactions
• What is an ionic bond?
• A bond between a metal and a nonmetal
• When forming an ion do metals become positive
or negative? Nonmetals?
• Metals give electrons and become positive
• Nonmetals receive electrons and become
negative
Oxidation Number
• The charge that the ion gets when it either
loses or gains electrons is called the oxidation
number.
The sum of the oxidation numbers for the
atoms in a compound must be zero
In order for a compound to exist, it must be
electrically neutral
NaCl
Sodium loses one
electron so it has
an oxidation
number of 1+
Na 1+
Chlorine gains one
electron so it has
an oxidation
number of 1-
Cl 1-
This works because 1(1+) + 1(1-) = 0
The sum of the oxidation numbers for the
atoms in a compound is zero
Li2O
Lithium loses one
electron so it has an
oxidation number of
1+
Li
1+
Oxygen gains two
electrons so it has
an oxidation number
of 2-
O 2-
This works because 2(1+) + 1(2-) = 0
The sum of the oxidation numbers for the
atoms in a compound is zero
Do now
• Determine the formula of a compound formed
from:
• Na and Cl
• Ca and S
• Au and O
• Al and S
Criss-Cross Method Shortcut
The ‘criss-cross’ method is a simple
way of determining a formula
 The oxidation number of one element
becomes the subscript of the other
Li +1
and
O -2
‘Criss - Cross’ Method
The formula for the
compound composed
of potassium and
sulphur
 K 1+ & S 2This becomes K2S
The formula for the
compound composed
of calcium and
bromine
 Ca 2+ & Br 1This becomes CaBr2
Steps to follow
• Step 1- write element symbols with the metal
first
• Step 2- write the oxidation numbers next to the
elements
• Metals = valence electron number (with a (+)
sign)
• Nonmetals = (valence electron #) – 8
• Step 3- criss-cross numbers without signs
• Step 4- don’t write 1’s for final compound
• Step 5- reduce the numbers.
‘Criss-Cross’ Method Practice
Using Oxidation
Numbers, write
formulas for the
compounds formed
from the following
elements
 Sodium & Bromine
 Potassium & Iodine
 Calcium & Fluorine
 Hydrogen & Sulfur
 Magnesium & Fluorine
 Lithium & Sulfur
Remember to check that the sum of the oxidation
numbers is equal to zero!
NaBr
KI
CaF2
H2S
MgF2
Li2S
DO NOW
• What is the formula of the compound formed
when copper and sulfur combine?
Naming Compounds
Binary Compounds are composed of two
elements
 Binary Compounds are named beginning with the
element with the positive oxidation number
(The Metal)
 The name of the second element will end in an ide
NaCl : Sodium Chloride
CaS : Calcium Sulfide
FeO : Iron Oxide
Name the Compound
•
•
•
•
•
•
1. Potassium + Nitrogen
2. Magnesium + Arsenic
3. Gallium + Phosphorous
4. Indium + Iodine
5. Barium + Fluorine
6. Aluminum + Oxygen
Covalent Bonds
• A bond between two nonmetals.
• Electrons are shared instead of transferred to
make the compound stable.
ex: H + H  H2