virtually everything that is, is made up of atoms
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Virtually everything that is, is made up of atoms.
Atomic Structure
Chapter 12, page 361
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Sub-Particles in the Atom
Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components.
Element = made of one kind of Atom. Li
Compounds = made of different atoms chemically bonded in whole number ratios.
H2O•Mixtures are physical combinations of elements or compounds with variable composition
O2 + H2.
Particles or Pure substances
Sub-Particle Mass Charge Locationin the Atom
proton ~1 a.m.u. 1+ in nucleus
neutron ~1 a.m.u. 0 in nucleus
electron ~0 a.m.u. 1- orbits nucleus
Sub-Particles in the Atom
atomic.mass.unit= a.m.u. ~ 1.992 ×10−27 kg or 1/12 the mass of C-12
Size of an atom
• Atoms are incredibly tiny.• Measured in picometers (10-12 meters)
– Hydrogen atom, 32 pm radius• Nucleus tiny compared to atom
– Radius of the nucleus near 10-15 m.– Density near 1014 g/cm3
• IF the atom was the size of a stadium, the nucleus would be the size of a marble.
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What holds an atom together?
• Nuclear Tug-Of-War• • Electrostatic force – like charges repel and un-like charges
attract
• Strong Nuclear Force – holds nucleons (p+ & n0)• together, very strong nuclear force but over short distances
– Stable nuclei are SMALL– Large nuclei tend to be unstable (radioactive)
• • Electrostatic Force• – Holds electrons on atom
Counting Particles in Atoms
Atomic Number = number of protons (p+) = unique for each element
Atomic Mass Number = Mass of an atom =number of protons + neutrons = (p+) + (no); (e- do not have mass)
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126C 14
6C
126C
Mass Number = A
Atomic Number = Z
How can I remember how many protons or electrons there are?Just remember the A.P.E. rules!
•atomic number =
•number of protons =
•number of electrons
A
P
E
Now, how do I remember how many protons there are?
Just remember the M.A.N.!•mass number -
•Atomic number =
•number of neutrons
M
A
N
Neon
Ne
Protons:
Electrons:
Neutrons:
Atomic Number: 10
Atomic Mass: 20
10
10
10
Phosphorus
P
Protons: 15
Electrons:
Neutrons: 16
Atomic Number:
Atomic Mass:
15
15
31
Aluminum
Al
Protons:
Electrons: 13
Neutrons: 14
Atomic Number:
Atomic Mass:
13
13
27
Argon
Ar
Protons: 18
Electrons:
Neutrons:
Atomic Number:
Atomic Mass: 40
18
18
22
Silicon
Si
Protons:
Electrons:
Neutrons: 14
Atomic Number: 14
Atomic Mass:
14
14
28
Symbols
Contain the symbol of the element, the mass number and the atomic number (top heavy)
X Massnumber
Atomicnumber
# protons
# protons + # neutrons mass number
Symbols
• Find the – Atomic number– Mass number– number of electrons– number of protons– number of neutrons
F19 9
= 9
= 10
= 9
= 9
= 19
+
So let’s practice!
Symbols
Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass number
Br8035
= 35
= 45
= 35
= 35
= 80
http://www.chem.purdue.edu/gchelp/liquids/bromine.gif
Symbols
Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass number
Na2311
Sodium atom
= 11
= 12
= 11
= 11
= 23
To find net charge on an atom, consider the p+ and the e–.
cation: a (+) ion-- more p+ than e–
-- formed when atoms lose e–
anion: a (–) ion -- more e– than p+ atoms -- formed when gain e–
ion: a charged atom
- -+++- -+
++
-
-
e-
p+
n0
-
+ + +
-+3 and -4 = -1
- - e-
p+
n0
-
+ + +
-+3 and -2 = +1
Ions
Symbols
Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass number
Na2311
1+
Sodium ion
= 11
= 12
= 10
= 11
= 23
Look
Symbols
If an element has an atomic number of 23 and a mass number of 51 what is the – number of protons– number of neutrons– number of electrons– Complete symbol
V5123
= 23
= 28
= 23
Symbols
If an element has 60 protons and 84 neutrons what is the – Atomic number– Mass number– number of electrons– Complete symbol
Nd14460
= 60
= 144
= 60
Symbols
If a neutral atom of an element has 78 electrons and 117 neutrons what is the – Atomic number– Mass number– number of protons– Complete symbol
Pt19578
= 78
= 195
= 78
Mass Number
• mass number= protons + neutrons
• always a whole number• NOT on the
Periodic Table!
+
+
+
+
+
+
NucleusElectrons
Nucleus
Neutron
Proton
Carbon-12Neutrons 6Protons 6Electrons 6
e-
e-
e-
e-
e-
e-
Isotopes
• Atoms of the same element with different mass numbers.
Mass #
Atomic #
• Nuclear symbol:
• Hyphen notation: carbon-12Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
12
6 C
Isotopes
• Dalton was wrong.• Atoms of the same element can have different
numbers of neutrons.• different mass numbers.• called isotopes.
Isotopes
+
+
+
+
+
+
NucleusElectrons
Nucleus
Neutron
Proton
Carbon-12Neutrons 6Protons 6Electrons 6
Nucleus
Electrons
Carbon-14Neutrons 8Protons 6Electrons 6
+
+
+
+
+
+
Nucleus
NeutronProton
What is an isotope?same number of protons, different numbers of neutrons.
Boron-10
B
Protons:
Electrons:
Neutrons:
Atomic Number: 5
Atomic Mass:10
Boron-11
B
Protons:
Electrons:
Neutrons:
Atomic Number: 5
Atomic Mass:11
5
5
5
5
5
6
B-10
10B 5
B-11
11B 5
Carbon-
C
Protons:
Electrons:
Neutrons: 6
Atomic Number: 6
Atomic Mass:
What is the average atomic mass of Carbon?
Carbon-
C
Protons: 6
Electrons:
Neutrons:
Atomic Number:
Atomic Mass:14
6
6
12
6
8
6
12 14
Isotopes
• Chlorine-37– atomic #:
– mass #:
– # of protons:
– # of electrons:
– # of neutrons:
17
37
17
17
20
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Cl17
37
37
17 Cl
Writing Isotopes• Put the mass number after the name of the
element• carbon- 12• carbon -14• uranium-235
– Or
California WEB
12
6 CMass #
Atomic #
12
6 C
Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart:
Element Symbol AtomicNumber
Mass#
# of protons
# of neutron
# of electron
charge
8 8 8
Potassium 39 +1
Br 45 -1
30 65 30
Atomic Number = Number of Protons
Number of Protons + Number of Neutrons = Atomic Mass
Atom (no charge) : Protons = Electrons
Ion (cation) : Protons > Electrons Ion (anion) : Electrons > Protons
Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart:
Element Symbol AtomicNumber
Mass#
# of protons
# of neutron
# of electron
charge
8 8 8
Potassium 39 +1
Br 45 -1
30 65 30
Oxygen
Bromine
Zinc
O
K
Zn
8
19
35
16
80
19
35
30
20
35
18
36
0
0
Atomic Number = Number of Protons
Number of Protons + Number of Neutrons = Atomic Mass
Atom (no charge) : Protons = Electrons
Ion (cation) : Protons > Electrons Ion (anion) : Electrons > Protons
A N S W E R K E Y
Isotopes
• Because of the existence of isotopes, the mass of a collection of atoms has an average value.
• Average mass = ATOMIC WEIGHT = ATOMIC MASS
• Boron is 20% B-10 and 80% B-11. – That is, B-11 is 80 percent abundant on earth.
• For boron atomic mass= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
Average Atomic Mass
• massed average of all isotopes on the Periodic Table
• round to 2 decimal places
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Avg.AtomicMass
= (mass)(%) + (mass)(%)
100
Average Atomic Mass
• EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% O-16, 0.04% O-17, and 0.20% O-18.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Avg.AtomicMass
= (16)(99.76) + (17)(0.04) + (18)(0.20)
100= 16.00
amu
Average Atomic Mass• EX: Find chlorine’s average atomic mass if approximately 8
of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Avg.AtomicMass
= (35)(8) + (37)(2)
10= 35.40 amu
• Assume you have only two atoms of chlorine.• One atom has a mass of 35 amu (Cl-35)• The other atom has a mass of 36 amu (Cl-36)
• What is the average mass of these two isotopes?35.5 amu
• Looking at the average atomic mass printed on the periodic table...approximately what percentage is Cl-35 and Cl-36?
55% Cl-35 and 45% Cl-36 is a good approximation
Cl35.453
17
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