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Definition of Atoms
• Atoms are the fundamental building blocks of all matter, not able to be split by ordinary chemical reactions
• greek word atomos which means “indivisible”. This is based upon the discontinuous theory of matter. (meaning matter can not continually be split and still remain the same)
HISTORY OF THE ATOMHISTORY OF THE ATOM
460 BC Democritus develops the idea of atoms
he pounded up materials in his pestle and
mortar until he had reduced them to
smaller and smaller particles which he
called
ATOMAATOMA
(greek for indivisible)
HISTORY OF THE ATOMHISTORY OF THE ATOM
• Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air.
• Aristotle was wrong. However, his theory persisted for 2000 years.
Aristotle
fire
air
water
earth
350 BC
HISTORY OF THE ATOMHISTORY OF THE ATOM
1808 John Dalton
suggested that all matter was made up of
tiny spheres that were able to bounce
around with perfect elasticity and called
themATOMIC THEORYATOMIC THEORY
• All matter is made of atoms.• Atoms of an element are identical.• Each element has different atoms.• Atoms of different elements combine in
constant ratios to form compounds.• Atoms are rearranged in reactions
HISTORY OF THE ATOMHISTORY OF THE ATOM
1898 Joseph John Thompson
found that atoms could sometimes eject a
far smaller negative particle which he
called an
ELECTRONELECTRON
HISTORY OF THE ATOMHISTORY OF THE ATOM
Thompson develops the idea that an atom was made up of
electrons scattered unevenly within an elastic sphere
surrounded by a soup of positive charge to balance the
electron's charge
1904
like plums surrounded by pudding.
PLUM PUDDING
MODEL
HISTORY OF THE ATOMHISTORY OF THE ATOM
1910 Ernest Rutherford
oversaw Geiger and Marsden carrying out
his famous experiment.
they fired Helium nuclei at a piece of gold
foil which was only a few atoms thick.
they found that although most of them
passed through. About 1 in 10,000 hit
HISTORY OF THE ATOMHISTORY OF THE ATOM
gold foil
helium nuclei
They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to
their surprise, some helium nuclei bounced straight back.
helium nuclei
HISTORY OF THE ATOMHISTORY OF THE ATOM
Rutherford’s new evidence allowed him to
propose a more detailed model with a
central nucleus.
He suggested that the positive charge
was all in a central nucleus. With this
holding the electrons in place by electrical
attraction
However, this was not the end of the story.
HISTORY OF THE ATOMHISTORY OF THE ATOM
1913 Niels Bohr
studied under Rutherford at the Victoria
University in Manchester.
Bohr refined Rutherford's idea by
adding that the electrons were in
orbits. Rather like planets orbiting the
sun. With each orbit only able to
contain a set number of electrons.
Bohr’s Atom
electrons in orbits
nucleus
Bohr’s Planetary Model of Atomanother look
HELIUM ATOM
+N
N
+-
-
proton
electron
neutron
Shell
What do these particles consist of?
ATOMIC STRUCTUREATOMIC STRUCTURE
Particle
proton
neutron
electron
Charge
+ 1 charge
-1 charge
0
1amu
1amu
1/1836
Mass
• Amu = atomic mass unit
• 1 amu = 1.66 x 10-24g
Relative Sizes
• Thus 99.99% of the mass of an atom comes from the nucleus (protons and neutrons) and essentially nothing from e-
• the major volume of atoms coming from the electron cloud
• Remember that most of the atom is empty space like spinning blades of a fan take up more space than any blade would if not moving
ATOMIC STRUCTUREATOMIC STRUCTURE
the number of protons and neutrons in an atom
the number of protons in an atom
HeHe44
22 Atomic number
Atomic mass
number of electrons = number of protons
Calculating subatomic particles
• p+ = atomic number
• n0 = mass # - p+
because mass of atom is p+ + n0
get the mass # by rounding average atomic mass on
periodic table to nearest whole number if needed
• e- = p+ - charge
because charge of atom/ion is p+ - e-
Protons, Electrons, NeutronsProtons, Electrons, Neutrons
Determine the number of protons, electrons and neutrons for each of the following elements;
Ca O
Cl Si
Na40
20
23
11
16
35
8
17
28
14B
5
11
a) b) c)
d) e) f)
P=20 e=20
n=20
p=11 e=11n=12
p=17 e=17n=18
p=14 e=14n=14
p=5 e=5n=6
p=8 e=8n=8
Equations: Protons = atomic #, neutrons = mass # - protons, electrons = protons with a neutral atom (charge = 0) electrons = protons – charge with a ion (charged atom)
Symbol protons Mass # neutrons electrons
7Li atom 3 p+
the atomic #7 amu 7-3 = 4 n0 3 e-
(same as p+)
Cs atom
Rb atom
32Cl-1 ion
Al-3 ion
42Ca+2 ion
Equations: mass # = atomic mass rounded to nearest whole Protons = atomic # Neutrons = mass # - protons with a neutral atom (charge = 0) the electrons = protons, with a ion (charged atom) the electrons = protons – net charge
Symbol protons Mass # neutrons electrons
7Li atom 3 p+ the atomic #
7 amu 7-3 = 4 n0 3 e- (same as p+)
Cs atom 55 133 78 55
Rb atom 37 85 48 37
32Cl-1 ion 17 32 15 18
Al-3 ion 13 27 14 16
42Ca+2 ion 20 42 22 18
IsotopesIsotopes
Carbon-12
Carbon-13
Carbon-14
Protons
6
6
6
6
7
8
Neutrons Mass #
12
13
14
• Atoms with same atomic number (number of protons), but with different masses (due to different number of neutrons)
12-6 = 6 13-6 = 7 14-6 = 8
Lithium Isotopes• Li-6 is the chemical symbol
for Lithium with a mass number of 6 amu. (this is 3 protons plus 3 neutrons in nucleus.
• Li-7 has 3 protons and 4 neutrons in nucleus and a mass of 7 amu.
• The atomic mass (or average weight) of Lithium is 6.941. Therefore which isotope is most abundant in nature?
IsotopesIsotopes
Lithium-8
Lithium-9
Lithium-11
Protons
3
3
3
5
6
8
Neutrons Mass #
8
9
11
8 - 3 = 5 9 - 3 = 6 11 – 3 = 8
IONSIONS
• IONSIONS are atoms or groups of atoms with a positive or negative chargeare atoms or groups of atoms with a positive or negative charge. .
•Taking awayTaking away an electron from an atom gives a an electron from an atom gives a CATIONCATION with with
aa positive chargepositive charge
• AddingAdding an electron to an atom gives an an electron to an atom gives an ANIONANION with awith a negative negative
chargecharge..• To tell the difference between an atom and an ion, look to see if there is a To tell the difference between an atom and an ion, look to see if there is a
charge in the superscript! Examples: Nacharge in the superscript! Examples: Na++ Ca Ca+2+2 I I-- O O-2-2
Na Ca I ONa Ca I O
Forming Cations & AnionsForming Cations & Anions
• A A CATIONCATION forms when an forms when an atom losesatom loses one or more electrons.one or more electrons.
Mg --> Mg2+ + 2 e-
An An ANIONANION forms when an forms when an atom gainsatom gains one one or more electronsor more electrons
F + e- --> F-
PREDICTING ION CHARGESPREDICTING ION CHARGES
In generalIn general
• metalsmetals (Mg) (Mg) lose electrons lose electrons --->--->cationscations
• Nonmetals Nonmetals (F) (F) gain electronsgain electrons anionsanions
Ion Practice
State the number of protons, neutrons, and electrons in each of these ions.
39 K+ 16O -2 41Ca +2
19 8 20
#p+ 19 8 20
#no 20 8 21
#e- 18 10 18
Charges on Common Charges on Common IonsIons -1-2-3
+1
+2
By losing or gaining e-, atom has same By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.number of e-’s as nearest Group 8A atom.
Special Family Names on the Periodic TableAlkali Metals = hot orange Semimetals/Metalloids = pinkAlkaline Earth Metals = Faded Blue Halogens = YellowTransition Metals = Indigo Noble Gases = Pumpkin OrangeOther Metals = Baby Blue Other Nonmetals = Green
3 p+
4 n02e– 1e–
Li shorthand
Bohr - Rutherford diagrams• Putting all this together, we get B-R diagrams• To draw them you must know the # of protons,
neutrons, and electrons (2,8,8,2 filling order)• Draw protons (p+), (n0) in circle (i.e. “nucleus”)• Draw electrons around in shells
2 p+
2 n0
He
3 p+
4 n0
Li
Draw Be, B, Al and shorthand diagrams for O, Na
11 p+12 n°
2e– 8e– 1e–
Na
8 p+8 n°
2e– 6e–
O
4 p+5 n°
Be
5 p+6 n°
B
13 p+14 n°
Al
ATOMIC STRUCTUREATOMIC STRUCTURE
Electrons are arranged in Energy Levels
or Shells around the nucleus of an atom.
• first shell a maximum of 2 electrons
• second shell a maximum of 8
electrons
• third shell a maximum of 8
electrons
ATOMIC STRUCTUREATOMIC STRUCTURE
There are two ways to represent the atomic
structure of an element or compound;
1. Electronic Configuration
2. Dot & Cross Diagrams
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
With electronic configuration elements are
represented numerically by the number of
electrons in their shells and number of shells. For
example;
N
Nitrogen
14
7
2 in 1st shell
5 in 2nd shell
configuration = 2 , 5
2 + 5 = 7
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements;
Ca O
Cl Si
Na40
20
23
11
16
35
8
17
28
14B
5
11
a) b) c)
d) e) f)
2,8,8,2 2,8,1
2,8,7 2,8,4 2,3
2,6
DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
With Dot & Cross diagrams elements and
compounds are represented by Dots or Crosses to
show electrons, and circles to show the shells. For
example;
Nitrogen N XX X
X
XX
X
N14
7
DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS
Draw the Dot & Cross diagrams for the following elements;
O Cl16 35
8 17a) b)
O
X
XX
X
X
X
X
X
Cl
X
X
X
X X
X
XX
X
X
X
X
X
XX
X
X
X
SUMMARYSUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus.
2. The Atomic Mass of an atom = number of
Protons + Neutrons in the nucleus.
3. The number of Protons = Number of Electrons.
4. Electrons orbit the nucleus in shells.
5. Each shell can only carry a set number of electrons.
