Transcript Revision for TY Chemistry Christmasx1mb

ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge
1
neutron
No charge
1
electron
-ve charge
nil
Atomic Number = Number of Protons
Always the smaller of the 2 numbers
can be on the top or bottom
Atomic Number
Symbol
11
Na
LecturePLUS Timberlake
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Number of Electrons
 An atom is neutral
 The net charge is zero
 Number of protons = Number of electrons
 Atomic number = Number of electrons
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Mass Number = Number of Neutrons
and Protons
 Show the mass number and atomic number
 Give the symbol of the element
mass number
23 Na
sodium-23
atomic number 11
LecturePLUS Timberlake
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SUMMARY
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.
What is a chemical equation?
• Chemical equation - Describes a chemical
change.
• Parts of an equation:
Reactant
Product
2Ag + H2S
Ag2S + H2
Reaction
symbol
Reactants and Products
• Reactant - The chemical(s) you start with
before the reaction.
– Written on left side of equation.
• Product - The new chemical(s) formed by the
reaction.
– Right side of equation.
Subscripts and Coefficients
• Subscript - shows how many atoms of an
element are in a molecule.
– EX: H2O
• 2 atoms of hydrogen (H)
• 1 atom of oxygen (O)
• Coefficient - shows how many molecules
there are of a particular chemical.
– EX: 3 H2O
• Means there are 3 water molecules.
Law of Conservation of Mass
• In a chemical reaction, matter is neither
created nor destroyed.
– In other words, the number and type of atoms
going INTO a reactionn must be the same as the
number and type of atoms coming OUT.
• If an equation obeys the Law of Conservation,
it is balanced.
An Unbalanced Equation
• CH4 + O2  CO2 + H2O
Reactant Side
1 carbon atom
4 hydrogen
atoms
2 oxygen atoms
Product Side
1 carbon atom
2 hydrogen
atoms
3 oxygen atoms
A Balanced Equation
 CH4 + 2O2  CO2 + 2H2O
Reactant Side
1 carbon atom
4 hydrogen
atoms
4 oxygen atoms
Product Side
1 carbon atom
4 hydrogen
atoms
4 oxygen atoms
Rules of the Game
Write down the correct formula given to you!
Find the number of atoms on the left and on the right.
Remember matter cannot be created or destroyed.
Subscripts cannot be added, removed, or changed.
You can only change coefficients.
Coefficients can only go in front of chem. formulas...NEVER in the
middle of a formula.
A few extra tips:
Try balancing big formulas first; save free elements for last.
If the same polyatomic ion appears on both sides of the equation, it’s
usually okay to treat it as one unit.
There is no one particular way to balance equations. Some equations
are harder to balance than others and might require some creativity to
solve.
Questions
Balance the following equations:
(a) P2O5(s) + H2O(l)  H3PO4(aq)
Answer: P2O5(s) + 3H2O(l)  2H3PO4(aq)
(b) NO2(g) + H2(g)  NH3(g) + H2O(g)
Answer: NO2(g) + 3 ½ H2(g)  NH3(g) + 2H2O(g)
(c) SO2(g) + O2(g)  SO3(g)
Answer: 2SO2(g) + O2(g)  2SO3(g)
Main Energy Levels consist of
Sublevels
14
• Principal Energy Levels or shells
• Divided into sublevels of
differing energy
• Sublevels further divided into
divisions of equal energy
• called orbitals
15
Orbitals
• Region in space around the nucleus in
which electrons are most likely to be
found.
• An orbital can hold 2 electrons
• There are four types of orbitals;
classed according to their shapes
• s, p, d, and f orbitals
16
s orbitals
• spherical
• There is only one s orbital per main
energy level [shell]
• each s orbital can hold 2 electrons
• each s sub-level can hold 2 electrons
17
p orbitals
• dumb-bell shaped
• each p sublevel is made up of 3 orbitals
px , py , pz [mutually at right angles]
• each p sublevel can hold a total of 6
electrons.
• All the orbitals in a p sublevel have the same
energy i.e. px = py = pz
18
19
d orbitals
• complex in shape
• each d sublevel is made up of 5 orbitals
(each orbital can hold 2 e-)
• therefore each d sublevel can hold 10
electrons
• All orbitals in a d sublevel have the same
energy
20
Aufbau Principle
• electrons occupy the lowest available
energy level
• (Aufbau is German for construction or
building)
• Fill sublevels from the nucleus outwards
21
Order of filling of sublevels
1s
2s
2p
3s
3p
3d
4s
4p
4d 4f
5s
5p
5d 5f
Need to know first
36
shown in yellow
22
Example
• Sodium 1123 Na
• 11 electrons
1s2 2s2 2p6 3s1
23
• Scandium 2145 Sc
• 21 electrons
• 1s2 2s2 2p6 3s23p6 4s2 3d1
• Iron 2656 Fe
• 26 electrons
• 1s2 2s2 2p6 3s23p6 4s2 3d6
24
Reason
• p, d and f sublevels that are
• half filled or
• completely filled
• have extra stability
• therefore one of the electrons in the 4s
sublevel flips over into the 3d sublevel to
attain this stability
[You need to know the electron configuration
for the first 36 elements.]
25
Electron configuration of ions
26
What is an ion?
It is an atom with a charge
2 types
+ and –
- ions gain or take in electrons
For each electron taken in they gain a –
charge
• + ve ions give away or lose electrons
• For each electron they lose they gain a +
charge
•
•
•
•
•
•
27
Electron configuration of ions
•
•
•
•
•
Al3+
the 3+ tells us the Al has lost 3 electrons
27Al has 13 e- so Al3+ has 10 e13
1s2 2s2 2p6
Normally written as [1s2 2s2 2p6 ] 3+
N.B. only ions of first 20 asked
28
• Cl1• the 1 tells us the Cl has gained 1 e
35
1• 17 Cl has 17 e so Cl has 18 e
• 1s2 2s2 2p6 3s2 3p6
• normally written [1s2 2s2 2p6 3s2 3p6 ]1N.B. only ions of first 20 asked
29
2S
•
• the 2- tells us the S has gained 2 e• 1632S has 16 e- so S2- has 18 e• 1s2 2s2 2p6 3s2 3p6
• normally written [1s2 2s2 2p6 3s2 3p6 ]2N.B. only ions of first 20 asked
30
• Ca2+
• the 2+ tells us the Ca has lost 2 e•
40Ca
20
has 20 e- so Ca2+ has 18 e-
• 1s2 2s2 2p6 3s2 3p6
• normally written [1s2 2s2 2p6 3s2 3p6 ] 2+
N.B. only ions of first 20 asked
31
Test on
electron distribution
32
1. State Aufbau principle. [2] electrons
occupy the lowest available energy level
2. Give the s,p,d,f. configuration of this
element [2] 1s2, 2s2, 2p6, 3s2 etc
3. Give the s,p,d,f. configuration of Cu or Cr
[2]
4. Why is this configuration used? [3] Two
half filled sub levels / give more stability /
than a filled s and a not half filled p or d
5. What is an Ion? [2] Atom with a charge
33
6. What does a 3- charge tell you? [2] gained /
3 e7. When ions form what are they trying to
achieve? [2] Stability / e- pattern of nearest
Noble Gas
8. Give e- pattern of X 3+ [2] [1s2, 2s2 etc]3+
9. State Hund’s Rule of maximum multiplicity.
[3] When more than one orbital available /
orbitals filled singly / and then in pairs
10.What do Na+, Ne and F- have in common [2]
same e- pattern
34
Isotopes
 Atoms with the same number of protons, but
different numbers of neutrons.
 Atoms of the same element (same atomic
number) with different mass numbers
Isotopes of chlorine
35Cl
37Cl
17
17
chlorine - 35
chlorine
37
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Calculating Atomic Mass
 Percent(%) abundance of isotopes
 Mass of each isotope of that element
 Weighted average =
mass isotope1(%) + mass isotope2(%) + …
100
100
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Atomic Mass of Magnesium
Isotopes
24Mg
=
Mass of Isotope Abundance
24.0 amu
78.70%
25Mg
=
25.0 amu
10.13%
=
26.0 amu
11.17%
26Mg
Atomic mass (average mass) Mg = 24.3 amu
Mg
24.3
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Learning Check AT7
Gallium is a metallic element found in small
lasers used in compact disc players. In a sample
of gallium, there is 60.2% of gallium-69 (68.9
amu) atoms and 39.8% of gallium-71 (70.9 amu)
atoms. What is the atomic mass of gallium?
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Solution AT7
Ga-69
68.9 amu x 60.2 = 41.5 amu for
69Ga
100
Ga-71 (%/100)
70.9 amu x 39.8
=
28.2 amu for
=
69.7 amu
71Ga
100
Atomic mass Ga
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• In a sample of carbon, there is 98.93% of
carbon12 (12.000 amu) atoms and 1.07% of
carbon13 (13.003 amu) atoms. What is the
atomic mass of carbon?
Finding An Isotopic Mass
A sample of boron consists of 10B (mass 10.0
amu) and 11B (mass 11.0 amu). If the average
atomic mass of B is 10.8 amu, what is the %
abundance of each boron isotope?
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Assign X and Y values:
X = % 10B
Y = % 11B
Determine Y in terms of X
X
+
Y
= 100
Y = 100 - X
Solve for X:
X (10.0) + (100 - X )(11.0) = 10.8
100
100
Multiply through by 100
10.0 X + 1100 - 11.0X = 1080
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Collect X terms
10.0 X - 11.0 X = 1080 - 1100
- 1.0 X = -20
X
= -20
- 1.0
= 20 %
10B
Y = 100 - X
% 11B = 100 - 20% = 80% 11B
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Learning Check AT8
Copper has two isotopes 63Cu (62.9 amu) and
65Cu (64.9 amu). What is the % abundance of
each isotope? (Hint: Check periodic table for
atomic mass)
1) 30%
2) 70%
LecturePLUS Timberlake
3) 100%
46
Solution AT8
2) 70%
Solution
62.9X + 6490 = 64.9X = 6350
-2.0 X = -140
X = 70%
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Average Atomic Mass
• weighted average of all isotopes
• on the Periodic Table
• round to 2 decimal places
Avg.
(mass)(%) + (mass)(%)
Atomic =
100
Mass
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Average Atomic Mass
• EX: Calculate the avg. atomic mass of oxygen if its
abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20%
18O.
Avg.
(16)(99.76) + (17)(0.04) + (18)(0.20)
16.00
Atomic =
=
amu
100
Mass
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
The Atom
• Fundamental unit of matter
• Made up of components called subatomic
particles
–
–
–
Proton (positive charge)
Neutron (no electrical charge)
Electron (negative charge)
Nucleus
Electron
What Is Carbon?
• Carbon-14 is also referred to as:
–
–
C-14
Radiocarbon
• Types of carbon (isotopes)
Atomic mass
9
14
16
6
6
6
Atomic number
Unstable Isotopes (Atoms)
An atom is generally stable if the number of protons equals the number
of neutrons in the nucleus
Atom (Isotope)
Protons
Neutrons
Stable Carbon
6
6
Stable Nitrogen
7
7
Stable Oxygen
8
8
6
8
Carbon 14
Losing Your Identity: Radioactive Decay
The nucleus of an atom (decays) changes
into a new element
The proton number (atomic number) changes
14
14
6
7
How long does this take?
Carbon-14 and Half-Life?

The rate of decay is measured by how
long it takes for half an element to decay
(half-life)
• The half-life of C-14 is 5,730 years
Half-Life Illustration
Time = 0
C-14
11,460 years
2 half-lives
5,730 years
1 half-life
N-14
1/2
N-14
3/4
C-14
1/2
C-14
If C-14 is constantly decaying,
will we run out of C-14 in the atmosphere?
How Carbon-14 Is Produced
Cosmic Rays
(radiation)
Forms C-14
Collision with atmosphere
(N14)
C-14 combines with oxygen to form
carbon dioxide (CO2)
Remember…
Ordinary carbon (C-12) is found in the carbon
dioxide (CO2) in the air, which is taken up by
plants, which in turn are eaten by animals.
A bone, or a leaf or a tree, or even a piece of
wooden furniture, contains carbon.
When the C-14 has been formed, like ordinary
carbon (C-12), it combines with oxygen to give
carbon dioxide (14CO2), and so it also gets
cycled through the cells of plants and animals.
• We can take a sample of air, count how
many C-12 atoms there are for every C14 atom, and calculate the C-14/C-12
ratio.
• Because C-14 is so well mixed up with
C-12, we expect to find that this ratio is
the same if we sample a leaf from a
tree, or a part of the body.
Carbon-14 Life Cycle
Cosmic radiation
14
14
14
7
6
7
Carbon-14 is produced in the atmosphere
Carbon-14 decays into Nitrogen-14
Matter
• Matter is everywhere.
• Matter is anything that takes up
space and has mass.
• Matter is constantly experiencing
both chemical and physical changes.
What is a Physical Change?
• A physical change alters the form of a
substance, but does not change it to
another substance.
Example:
Making Orange Juice
What is a Chemical Change?
• When a substance undergoes a chemical
change, it is changed into a different
substance with different properties.
Example:
Baking a Cake
5 Signs of a Chemical Change
1. Color Change
2. Precipitation - the solid that forms from a
solution during a chemical reaction.
3. Gas Production
4. Temperature Change
5. Changes in Characteristic Properties (odor,
light given off)
I mole of a substance is the amount of that
substance which contains particles of that 6.0 x
1023 substance.
 Avogadro’s Number of particles = 6.0x1023
• 1 mole of oxygen = 16g
Definitions
RMM in grams – Relative
Molecular Mass
The RMM of a compound = Sum of
the molecular masses of the atoms
in the compound.
RMM in Grams
H2O = (2 x 1) + 16 = 18
(NH4)2SO4 = (14+1*4)*2+32+16*4 = 132
What is the RMM of each of the following
H3PO4 ; Al2(SO4)3 ; CuSO4.5H2O?
H3PO4 = 1 * 3 + 31 + 16 * 4 = 98
Al2(SO4)3 = 27 * 2 + (32 +16*4)*3 = 342
CuSO4.5H2O = 64 + 32 +16*4+ 5(1*2 +16) = 250
Questions
H3PO4 ; Al2(SO4)3 ; CuSO4.5H2O
• How many moles in 10 grams of each?
• What mass of each is needed to make 0.75 mole?
• H3PO4 = 10/98 = 0.1 mole
• Al2(SO4)3 = 10/342 = 0.03 mole
• CuSO4.5H2O 10/250 = 0.04 mole
• H3PO4 = 0.75 of 98 = 73.5 g
• Al2(SO4)3 = 0.75 of 342 = 256.5 g
• CuSO4.5H2O = 0.75 of 250 = 187.5 g
Avogadro’s Number = 6 x 1023
How many molecules are there in 5 g of each
of the following?
a) Hydrogen gas [H2]
b) Methane [CH4]
c) Water [H2O]
d) Ammonium nitrate [NH4NO3]
e) Calcium carbonate [CaCO3]
Grams
H2
1 mole
2g
1g
5g
Molecules
6 * 1023
23
6 * 10
23
6 * 10 / 2
5 * 6 * 1023/ 2
1.5 * 1024
Avogadro’s Number = 6 * 1023
How many atoms are there in 5 g of each of
the following?
a) Hydrogen gas [H2]
b) Methane [CH4]
c) Water [H2O]
d) Ammonium nitrate [NH4NO3]
e) Calcium carbonate [CaCO3]
• H2 = 1 * 2 = 2g 5/2 = 2.5 moles
= 2.5 * 6 * 1023 = 15 * 1023 * 2 = 3.0 *1024
• CH4 = 12 + (1*4) = 16 g5/16 = 0.31 mole
= 0.31 * 6 * 1023 = 1.88 * 1023 * 5 = 9.4 * 1023
• H2O = (1*2) + 16 = 18g 5/18 = 0.28 mole
= 0.28 * 6 * 1023 = 1.68 * 1023 * 3 = 5.04 * 1023
• NH4NO3 = 14 + (1*4) + 14 + (16*3) = 80 g
5/80 = 0.0625 mole = 0.0625 * 6 * 1023
= 0.375 * 1023 = 3.75 * 1022 * 9 = 3.38 * 1023
• CaCO3 = 40+12+(16*3) =100 = 5/100 = 0.05 mole
0.05*6*1023 = 0.3*1023 = 3.0*1022*5 = 1.5 * 1023
22.4 L of any gas at STP
• Volume occupied by each of the
following
• 8g of Oxygen
• 32g methane
• 20g of neon
• 7.1g of chlorine
• 0.01g of hydrogen
• O2 = 16 * 2 = 32 g  8/32 = 0.25 moles
0.25 of 22.4 L = 5.6 L
• CH4 = 12+ (1*4) = 16g  32/16 = 2 mole
= 2 * 22.4 l = 44.8 L
• Ne = 20 = 20g 20/20 = 1 mole
= 22.4 L
• Cl2 = 35.5 * 2 = 71 g  7.1/71 = 0.1 moles
0.1 of 22.4 L = 2.24 L
General rule for questions
• Write down the two units
• Put the one you are given the amount of first
and the one you are asked the amount of
second
• Give the value of 1 mole of each
• Bring the one you know the amount of down to
1 unit and divide the other by the molar amount
• Multiply both by the amount given
• Watch out for the number of atoms / molecules
Example
•
•
•
•
•
•
How many atoms in 2.24L of methane at STP?
22.4L = 6 * 1023 molecules
1L
= 6 * 1023 / 22.4 molecules
2.24L = 2.24 * 6 * 1023 / 22.4
Methane is CH4 so 5 atoms per molecule
Atoms = 5 * 2.24 * 6 * 1023 / 22.4 = 3 * 1023