Download Chemistry powerpoint notes

How are atoms studied?
• Atoms are the building blocks of matter
• Atoms are too small in size to study
easily
• Size of Earth : soda can = soda can : atom
Democritus
• Not until around 460 B.C., did a Greek
philosopher, Democritus, develop the idea
of atoms. He asked this question: If you
break a piece of matter in half, and then
break it in half again, how many breaks will
you have to make before you can break it no
further? Democritus thought that it ended at
some point, a smallest possible bit of
matter. He called these basic matter
particles, atoms.
Democritus
• He said in the world this was “atoms and
void”. No space between the atoms.
ATOMS
Atoms: smallest particle that matter can be
broken down.
Who studied the atom?
• Studied by many scientists for centuries
– Democritus (400 BC) – phrase “atomos”
– Rutherford (1911) – nucleus (gold foil expt)
– Moseley (1913) – X-rays to find atomic #
– Bohr (1913) – planetary model of the atom
– Schrödinger (1923) – electron cloud model
Thomson’s Plum Pudding Model
• In 1897, the
English scientist
J.J. Thomson
provided the first
hint that an atom
is made of even
smaller particles.
Thomson Model
• He proposed a
model of the atom
that is sometimes
called the “Plum
Pudding” model.
• Atoms were made
from a positively
charged substance
with negatively
charged electrons
scattered about, like
raisins in a
pudding.
Atoms, Molecules and Ions
John Dalton 1806
Atomic Theory of Matter
1. Matter consists of indivisible atoms
2. All atoms of a given element
have identical properties
3. Different elements have atoms that
differ in mass
4. Atoms are indestructible and chemical
reactions are a rearrangement of atoms
5. Compounds contain a definite and small number
of atoms
Discovery of the Atom
By the early 1800’s, John Dalton proposed that
all substances are made up of atoms.
In 1898, J.J. Thomson, proposed that atoms
are made up of smaller parts.
In 1911, Ernest Rutherford, proposed that atoms
have electrons and a positive charged nuclues.
Parts of an Atom
1. Proton - nucleus
2. Neutron – nucleus
3. Electron – shells
Protons and neutrons make up the nucleus and
has the most mass. Electrons do not weigh as
much.
Protons
Protons are located in the nucleus of the atom.
They are positively charged.
Neutrons
Neutrons are located in the nucleus.
They have NO charge!
Electrons
Electrons are located in the shells around
the atom.
They are negatively charged.
Ion – a charged atoms caused by the loss
or gain of an electron.
Atoms make up substances called
elements which are the building
blocks of matter.
There are 110 elements
1. ELEMENTS ARE PURE SUBSTANCES MADE OF
ONLY 1 KIND OF ATOM AND ARE THE BUILDING
BLOCKS OF MATTER.
2. ELEMENTS CANNOT BE BROKEN DOWN INTO A
SIMPLER SUBSTANCE
3. ELEMENTS HAVE THEIR OWN UNIQUE SET OF
PROPERTIES THAT NO OTHER ELEMENT HAS.
• ELEMENTS ARE MADE OF ONLY 1 KIND OF
ATOM
• SOME COMMON ELEMENTS
– HYDROGEN (H), HELIUM (He), OXYGEN (0),
– Notice that the first letter is capital and the next letter
is lower case.
Why Do Some Elements Have Different Symbols?
They are older elements that were name
in a different language like Latin.
Copper – cuprum
Iron – Ferrous
Gold - aurum
Silver - argentum
Elements in Organisms
• 4 elements that make up 96% of human
body: Carbon(C), Hydrogen(H),
Oxygen(O), Nitrogen(N)
Element Info in Each Box
Atomic weight
Atomic Number
Symbol
Name
Information from the periodic table
Atomic Number- Number of Protons
in an atom
Silver = 47 protons
Atomic Weight - total number of particles in an
atom's nucleus
Atomic Weight is not very helpful – you need to
find the atomic mass
To find the Atomic Mass:
Round the atomic weight
Krypton's mass
number is 84 since
its atomic weight,
83.80, rounds up to
84.
Mass Number = (Number of Protons) + (Number of Neutrons)
84 = 36 + 48
Ways the Periodic Table is Organized
1. ELEMENTS ARE ORGANIZED IN THE
PERIODIC TABLE ACCORDING TO
ATOMIC NUMBER
2. ELEMENTS ARE ORGANIZED IN THE
PERIODIC TABLE OF ELEMENTS
ACCORDING TO THEIR SIMILAR
CHARACTERISTICS
• 3 major groups: metals, nonmetals and metalloids
Arrangement of the Periodic table
3. Periods – Rows are called periods. The
Elements in these rows have the same number
of electron shells.
4. Groups – Columns are called groups. These
elements have the same properties because of
the number of valence electrons.
Even though they skip some squares in between,
all of the rows go left to right. When you look at a
periodic table, each of the rows is considered to be
a different period (Get it? Like PERIODic table.). In
the periodic table, elements have something in
common if they are in the same row. All of the
elements in a period have the same number of
electron shells. Every element in the top row (the
first period) has one orbital for its electrons. All of
the elements in the second row (the second period)
have two orbitals for their electrons. It goes down
the periodic table like that. At this time, the
maximum number of electron orbitals or electron
shells for any element is seven.
Groups
When a column
goes from top to
bottom, it's
called a group.
Groups are often called
families because these
elements seem to be
related.
**Elements in the same group show
similarities in their chemical and
physical properties.
Electron shells
a) Atomic number = number of Electrons
b) Electrons vary in the amount of energy
they possess, and they occur at certain
energy levels or electron shells.
c) Electron shells determine how an atom
behaves when it encounters other atoms
VALENCE ELECTRONS
• Number of electrons in the outermost.
Determines how the element will bond.
GROUPS: determined by valence
electrons.
Group 1 – one valence electron
Group 2 – 2 valence electrons
Valence Electrons
The number of valence electrons determines how
an atom will bond.
The behavior of an atom is determined by its
electrons.
Shell
Maximum Number
Numb
of Electrons in the Shell
er
1
2
3
4
5
2x1=2
2x4=8
2 x 9 = 18
2 x 16 = 32
2 x 25 = 50
Determining the valence electrons for some elements
Li – 3 electrons
2 e- in 1st level
1 e- in 2nd level
1 valence
electron
C – 6 electrons
2 e- in 1st level
4 e- in 2nd level
4 valence
electrons
Timberlake, Table 2.15 (7th Ed); Table 2.14 (8th Ed)
How do you calculate Valance Electrons?
You determine the number of electrons.
Then place the electrons in electron shells.
Bohr’s Model: This is a model used to place
electrons in their shells.
Bohr Diagrams
1) Find your element on the periodic table.
2) Determine the number of electrons – it is
the same as the atomic number.
3) This is how many electrons you will draw.
4) The number of shells are determined by
the period.
Bohr Diagrams
• Find out which period
(row) your element is in.
• Elements in the 1st
period have one energy
level.
• Elements in the 2nd
period have two energy
levels, and so on.
www.chem4kids.com
Bohr Diagrams
C
1) Draw a nucleus with the
element symbol inside.
2) Place Protons and neutrons in
the nucleus.
3) Carbon is in the 2nd period, so it
has two energy levels, or shells.
4) Draw the shells around the
nucleus.
Bohr Diagrams
C
1) Add the electrons.
2) Carbon has 6
electrons.
3) The first shell can
only hold 2 electrons.
Bohr Diagrams
C
1) Since you have 2
electrons already
drawn, you need to add
4 more.
2) These go in the 2nd
shell.
3) Add one at a time starting on the right
side and going counter
clock-wise.
Bohr Diagrams
C
1) Check your work.
2) You should have 6 total
electrons for Carbon.
3) Only two electrons can
fit in the 1st shell.
4) The 2nd shell can hold up
to 8 electrons.
5) The 3rd shell can hold
18, but the elements in
the first few periods only
use 8 electrons.
• MOLECULES ARE 2 OR MORE ATOMS
ATTACHED TOGETHER
– THEY CAN BE THE SAME KIND
(ELEMENTS)
– THEY CAN BE DIFFERENT KINDS
(COMPOUNDS)
Examples: H2O, NaCl.
• COMPOUNDS ARE MADE OF 2 OR MORE
KINDS OF ATOMS BONDED TOGETHER
• FOR A COMPOUND TO FORM, A CHEMICAL
CHANGE MUST TAKE PLACE (A REACTION)
• THE ELEMENTS THAT COMBINE MAKE A
NEW SUBSTANCE WITH NEW PHYSICAL
PROPERTIES
• COMPOUNDS CANNOT BE BROKEN DOWN
PHYSICALLY. REQUIRES A CHEMICAL
CHANGE
TABLE
• MORE COMMON THAN ELEMENTS
NaCl
SALT
+
=
• COMPOUNDS ARE MADE OF 2 OR
MORE DIFFERENT KINDS OF
ELEMENTS.
• COMPOUNDS ARE IDENTIFIED BY A
CHEMICAL FORMULA
NaCl
+
=
TABLE
SALT
Chemical Changes Through Chemical
Reactions
A chemical reaction – Process in which the
physical and chemical properties of the original
substance change as new substances with
different properties are formed
http://www.eepybird.com/dc
m1.html
Chemical Formula
Definition – Short way to write a compound
using symbols.
Subscript – Small number that is written
below the element.
Coefficient – The large number in front of the
symbols.
Counting Atoms in Compounds
In compounds you will see elements and in
some compound you will see small numbers
behind the elements, example H2O, that small
number is called a subscript. If the element
does not have a subscript behind it, the
subscript is 1.
- The subscript tells you how many of
those atoms are in that compound.
.
Counting Atoms in Compounds
If there is a parentheses in the compound
then you multiply the subscript behind the
parentheses by the subscript that is
behind the element in that parentheses.
Ba(OH)2 –
1) In this compound there are three different elements
(Barium Hydroxide) they are Barium (Ba), Oxygen (O) and Hydorgen
(H).
2) In this compound the subscript 2 goes with the
4. Oxygen is in the
parentheses and the two elements in the
paraentheses so there parentheses are Oxygen (O) and Hydrogen (H).
is 2. Same for Hydrogen.
3) Since Ba is not in the parentheses and it does not
have a subscript there is one Ba.
Why do elements bond?
• Elements bond to fill their outer shells.
This make the element stable.
• Elements will either gain, lose or share
electrons to fill their outer shell.
Three types of Chemical Bonds
•
Chemically combining of two or more
atoms
1. Covalent Bonds
2. Ionic Bonds
3. Hydrogen bonds
These are not all the bonds but all we are going to
cover.
Ionic Bonds
In an IONIC bond,
electrons are lost or gained,
resulting in the formation of IONS
in ionic compounds.
K
F
Ionic bonding
Ionic bonding involves 3 steps (3 energies)
1) loss of an electron(s) by one element,
2) gain of electron(s) by a second element,
3) attraction between positive and negative
Na
Cl
Cl–
Ionization energy
+ e–
+ Na+
e– + Na+
Electron affinity
Lattice energy
Cl–
Cl– Na+
Covalent Bonds
• One or more pairs of
electrons are shared
by two atoms
Covalent
Compounds
– Gases, liquids, or
solids
– Low melting and
boiling points
– Poor electrical
conductors
– Many soluble in
nonpolar liquids but
not in water
Ionic
Compounds
– Crystalline solids
– High melting and
boiling points
– Conduct electricity
when melted
– Many soluble in
water but not in
nonpolar liquid
Octet Rule = atoms tend to gain, lose or share electrons so
as to have 8 electrons
C would like to Gain 4 electrons
N would like to Gain 3 electrons
O would like to Gain 2 electrons
Single Covalent Bonds
• A single covalent bond is one in which
two atoms share a pair of electrons.
• Structural formulas are chemical
formulas that show the arrangement of
atoms in molecules and polyatomic ions.
– Chemical Formula
•
•
•
•
H2
H2O
NH3
CH4
Structural Formula
H-H