Unit 3 2 structure of the atom
Transcript of Unit 3 2 structure of the atom
Purpose
• Matter is made up of atoms, so it is very important to understand what an atom is and the difference between different atoms. In this lesson, we briefly discuss the composition of an atom and learn how to identify atoms, learn the differences between atoms of the same element and the differences between atoms of different elements. Additionally, we learn how to use the periodic table to determine some of this information.
An atom is made up of 3 particles
• Proton
– Positively charged particle
– In the nucleus
– Symbol: p+
• Neutron
– Uncharged particle
– In the nucleus
– Symbol: n0
• Electron
– Negatively charged particles
– Outside the nucleus
– Much lighter than protons and neutrons – approximately 1/2000th the mass of protons and neutrons
– Symbol: e-
Structure of an atom – protons and neutrons in the nucleus, electrons outside the nucleus
+++
+
-
- -
- +
-
proton
neutron
electronBeryllium atom
Note: This is not to scale – electrons are considerably smaller than protons and neutrons and the nucleus is quite a bit smaller than the overall size of the atom.
The type of atom is determined by the number of protons.
• Any atom with 4 protons is a beryllium atom.
• Any atom with 6 protons is a carbon atom
• The periodic table shows the names and symbols assigned to all known atoms and is organized based on the number of protons each atom contains.
• The number of protons is also called the atomic number (Z)
1 2
3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
87 88
57 58 59 60 61 62 63 64 65 66 67 68 69 70
lanthanides(rare earth metals)
89 90 91 92 93 94 95 96 97 98 99 100 101 102
actinides
Lu Hf Ta
Y Zr
52.00
Mnmanganese
54.94
Crchromium
Vvanadium
157.3
gadoliniumneodymium
138.9 144.2 145 150.4 152.0
266262 261
227
262
americiumactinium
lanthanum
Ac
cerium praseodymium
berkeliumCmTh Pa Pu Am
259247 247 251 252 257 258
fermium mendelevium
237 239 243
curiumNp No
232.0 231.0 238.0
MdCf EsUneptunium plutoniumthorium protactinium uranium nobelium
Bkcalifornium einsteinium
Fm
Ererbiumdysprosium
La Ce Pr Nd Pm Sm Gd
272 285
roentgentiumununbium
promethiumYb
ytterbium
173.0158.9 162.5
DyTbterbium
164.9 167.3
Tmthulium
168.9
Hoholmium
Uublawrenciumrutherfordiumdubnium seaborgium bohrium hassium
samarium europiumEu
meitneriumdarmstadtium
264 277 268 281
Lr Rf Db Sg Bh Hs Mt Ds Rg
iridium platinum gold mercury
175.0 178.5 180.9 183.8 186.2 190.2
lutetium hafnium tantalum tungsten rhenium osmium
192.2 195.1 197.0 200.6
technetium ruthenium rhodium palladium
98 101.1 102.9 106.4
yttrium zirconium
Os Ir Pt Au Hg
88.91 91.22 92.91 95.94 107.9 112.4
W
ununtriumununquadium
Mo Ag CdTc Ru Rh Pdmolybdenum
Tl Pb
106 107 108 109 110 111 112 113 114
silver cadmium
Re
284 289 288 292 294
astatine radon
210 222
ununpentiumununhexiumUup Uuh
ununoctium
204.4 207.2 209.0 209
UuoUut Uuq
Pothallium lead bismuth polonium
At Rn
Sb Te I Xe
126.9 131.3
antimony tellurium iodine xenon
69.72 72.64 74.92 78.96
germanium
79.90 83.80
114.8 118.7 121.8 127.6
arsenic selenium
indium tinIn Sn
30.97
As Kr
39.95
bromine
32.07 35.45
Araluminum silicon phosphorus sulfur chlorine argon
Si
28.09
BrSekrypton
Ga Ge
P S Cl
50.94
Nbniobium
Tititanium
47.87
Cucopper
63.55
Znzinc
65.41
iron
55.85
Cocobalt
58.93
Ninickel
58.69
gallium
Nnitrogen
14.01
Neneon
20.18
Ooxygen
16.00
Ffluorine
19.00
boron
10.81
Ccarbon
12.01
132.9 137.3
sodium
Fe
5
V B
22.99 24.31
Al
26.98
Ca
40.08
Scscandium
44.96
rubidium strontium
85.47 87.62
9.012
K
103 104 105
4.003
Li
Hhydrogen
1.008
13
III A
14
IV A
Mg 6
VI B
7
VII B
8
VIII B
12
II B
9
VIII B
10
VIII B
11
I B
15
V A
16
VI A
Be B
4
5
potassium calcium
39.10
18
VIII A
17
VII AHe
helium
Pe
rio
d
1
2
3
1
I A
lithium
Na
6.941
Rb Sr
2
II A
3
III B
4
IV Bmagnesium
beryllium
6
7
226
140.1 140.9
Fr
Cs Bacesium barium
Rafrancium radium
223
Bi
115 116 118
4
9.012
Beberyllium
Atomic Number gives the number of protons
Symbol
Name
Pause and Practice
• Use the periodic table to complete the table below:
Element Symbol
Element Name
Atomic Number
Number of protons
H Hydrogen 1 1
Mg 12
Iron 26
10
K
Pause and Practice - Answers
• Use the periodic table to complete the table below:
Element Symbol
Element Name
Atomic Number
Number of protons
H Hydrogen 1 1
Mg Magnesium 12 12
Fe Iron 26 26
Ne Neon 10 10
K Potassium 19 19
A note about periodic table symbols.
• Symbols can be one or two letters
– One letter symbols are always capitalized
• Hydrogen = H
• Oxygen = O
– Two letter symbols always have the first letter capitalized and the second letter lowercase
• Helium = He
• Calcium = Ca
Symbols you should know – memorize them!
• The first 20 element symbols
– Hydrogen = H
– Helium = He
– Lithium = Li
– Beryllium = Be
– Boron = B
– Carbon = C
– Nitrogen = N
– Oxygen = O
– Fluorine = F
– Neon = Ne
– Sodium = Na
– Magnesium = Mg
– Aluminum = Al
– Silicon = Si
– Phosphorus = P
– Sulfur = S
– Chlorine = Cl
– Argon = Ar
– Potassium = K
– Calcium = Ca
• Some other common elements to know
– Copper = Cu
– Iron = Fe
– Lead = Pb
– Silver = Ag
– Zinc = Zn
– Tin = Sn
– Mercury = Hg
– Bromine = Br
– Iodine = I
The following are the symbols that are missed most often. Pay particular attention to these.
• Sodium, silicon, and sulfur– Sodium = Na
– Silicon = Si
– Sulfur = S
• Phosphorus and Potassium– Phosphorus = P
– Potassium = K
• Metals with symbols derived from other languages.– Copper = Cu
– Iron = Fe
– Lead = Pb
– Silver = Ag
– Tin = Sn
– Mercury = Hg
Suggestion
• Make a set of flash cards with the name of the element on one side and their symbol on the other for the elements that you have been asked to learn.
The periodic table tells us how many protons are in every atom. What about electrons and neutrons?
• Electrons
– For a neutral atom, the number of electrons is the same as the number of protons so it can be determined by looking at the atomic number on the periodic table.
• Neutrons
– One cannot look at the periodic table and determine the number of neutrons in an atom.
– To know neutrons, you must be given the mass number
Mass number and number of neutrons
• Mass number (Z)
– The mass number is the total number of protons plus neutrons.
Z = #p+ + #n0
– Mass numbers must be given to you, or you must be told the number of neutrons in the atom.
• The reason for this is that while a neutral atom of carbon will always have 6 protons and 6 electrons, it can have 6, 7, or 8 neutrons.
Isotopes are atoms of an element that differ in the number of neutrons they contain.
• All carbon atoms have 6 protons
– Most carbon atoms have 6 neutrons and are named carbon-12
– Some carbon atoms have 7 neutrons and are named carbon-13
– A few carbon atoms have 8 neutrons and are named carbon-14
• The number after the name is the mass number, which represents the sum of the protons and neutrons
Pause and Practice
• An atom has 19 protons and 21 neutrons. What is its mass number? What is its name?
• An atom has a mass number of 37 and contains 17 protons. What is the name of the atom, and how many neutrons does it contain?
Pause and Practice Answers
• An atom has 19 protons and 21 neutrons. What is its mass number? What is its name?
– Mass number: 40
– Name: potassium-40
• An atom has a mass number of 37 and contains 17 protons. What is the name of the atom, and how many neutrons does it contain?
– Name: chlorine-37
– Number of neutrons: 20
Misconception Alert
• You cannot get mass numbers off the periodic table.
• The mass shown on the periodic table will be discussed in a later unit. In short, it is the average mass of all the isotopes of that element – it does not represent any particular atom.
• For example, if we asked how many protons and neutrons are in a chlorine atom, you would look at the periodic table and see that it has an atomic number of 17. It therefore has 17 protons. You cannot answer how many neutrons without being told more information.
We can show atomic number and mass number with the symbols
• Carbon-12 has 6 protons, 6 neutrons, and a mass number of 12. We can represent it with the following symbol:
612𝐶
• When writing symbols this way, the mass number(A) goes on the upper left and the atomic number(Z) goes on the lower left of the symbol(X).
𝑍𝐴𝑋
Pause and Practice - Fill in the table
Complete Symbol
Name Number of protons
Number of neutrons
Number of electrons
Atomic Number
Mass Number
612𝐶 Carbon-12 6 6 6 6 12
Hydrogen-1
16 20 16
7 15
2046𝐶𝑎
Pause and Practice Answers
Complete Symbol
Name Number of protons
Number of neutrons
Number of electrons
Atomic Number
Mass Number
612𝐶 Carbon-12 6 6 6 6 12
11𝐻 Hydrogen-1 1 0 1 1 1
1636𝑆 Sulfur-36 16 20 16 16 36
715𝑁 Nitrogen-15 7 8 7 7 15
2046𝐶𝑎 Calcium-46 20 26 20 20 46