unit 2 atomic number, mass number and isotopes. homework complete worksheet 4a read pages 29-31 ...
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Unit 2
Atomic Number, Mass Number and Isotopes
Homework
Complete worksheet 4ARead Pages 29-31Chapter 2 problems: 8, 10, 14,16Test scheduled for Nov. 17, 18 and 19
(Wed., Thursday or Friday)
Distinguishing Between Atoms
Atomic Number– Unique for each element.
– Equal to the number of protons in the nucleus of an atom of that element.
– The number of protons must equal the number of electrons.
Distinguishing Between Atoms
Mass Number– Mass is concentrated in the nucleus
– Depends on the number of protons and neutrons.
Distinguishing Between Atoms
Determining atomic composition from mass number and atomic number– Number of protons = number of electrons
= Atomic number
– Number of neutrons = mass number – number of protons.
Distinguishing Between Atoms
Representing atomic composition using atomic number and mass number
Distinguishing Between Atoms
Elements can also be represented using name and mass number– Carbon - 12
Distinguishing Between Atoms
Element Symbol Atomic # Mass # # of Neutrons
Nitrogen-15
Neon-22
Beryllium-9
Distinguishing Between Atoms
Element Symbol Atomic
#
Mass # # of
Protons
# of
Electrons
# of
Neutrons
Carbon 12 6
K 19 21
12 12 12
Helium 2 4 2
5 5 6
Mercury 80 120
Distinguishing Between Atoms
Isotopes– Equal number of protons and electrons.
– Different number of neutrons
– Different mass number
Chemically alike
Distinguishing Between Atoms
Atomic Mass– Mass of proton or neutron is small
(1.67 x 10-24 g)
– Mass of electron is negligible in comparison (9.11 x 10-28 g)
The mass of even the largest atom is incredibly small
Distinguishing Between Atoms
Compare relative mass using a reference isotope as a standard
Isotope C-12 assigned a mass of 12 amu
Atomic mass unit (amu) defined as one-twelfth the mass of carbon-12
Distinguishing Between Atoms
If atomic mass is determined by the number of protons and neutrons, why isn’t the mass of an element a whole number?
Most elements occur as a mixture of two or more isotopes.
Isotopes of hydrogen
Hydrogen – 1 (protium 99.98%)Hydrogen – 2 (deuterium
0.0156%)Hydrogen – 3 (tritium trace
quantities)
Protium
1 proton1 electron0 neutrons
Deuterium 1 proton, 1electron, 1neutronD2O = heavy water
Concentrated with neutrons during slow electrolysis of water
Greater density and higher boiling point then H2O
Not radioactive
Tritium1 proton, 1 electron, 2 neutronsFormed continuously in upper
atmosphere in nuclear reactions by cosmic rays
Compounds can be labeled with D or T by comparing the location of the heavy Hydrogen
Distinguishing Between Atoms
The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.
Distinguishing Between Atoms
You can calculate the atomic mass if you know three values:– The number of stable isotopes of the
element.
– The mass of each isotope.
– The natural percent abundance of each isotope.
Distinguishing Between Atoms
Chlorine, symbol Cl, has two isotopes– Cl-35 (34.97) abundance 75.77%
– Cl-37 (36.97) abundance 24.23%
Calculate the atomic mass of chlorine
4A Atomic Structure
1. 12
2. 12
3. 12.0 amu
4a. 5 b. 16 c. 38 d. 79
5a. hydrogen c. lithium
b. iron d. argon
7. 6.95 amu
4A Atomic Structure
element # of p+ # of e- # of n0 atomic # mass #manganese Mn 25 25 30 25 55
sodium Na 11 11 12 11 23
bromine Br 35 35 45 35 80
yttrium Y 39 39 50 39 89
arsenic As 33 33 42 33 75
actinium Ac 89 89 138 89 227
Chapter 2
8. 86 protons, 134 neutrons
10. Fe Fe
14. a. 34 b. 41 c. 34
d. 41 n0, 34p+, 36e-
5426
5626
Chapter 2 #16
symbol charge protons neutrons electrons
Br 0 35 44 35
N3- -3 7 7 10
As5+ +5 33 42 28
Zr4+ +4 40 50 36
7935
147
7533
9040
Homework
Read Chapter 2 pages 33-35WS: 5.4 The Periodic TableChapter 2: problems 20, 22, 24 and 26Webassign Due Nov. 19Test: Nov. 17, 18 19 (Wed. Thurs. Fri)
The Periodic Table
Dmitri Mendeleev (1834-1907)– Russian chemist
– Listed elements in columns in order of increasing atomic mass.
– Arranged columns so that elements with similar properties were side by side.
The Periodic Table
Mendeleev left blank spaces where there were no known elements with the appropriate properties or mass.
Predicted the properties of the missing elements.
THE PERIODIC TABLE
Dmitri Mendeleev (1834-1907)
Henry Mosely (1887-1915)Determined atomic numbers of
the elements.Arranged elements in table by
atomic number instead of mass.
THE PERIODIC TABLE
Henry Mosely (1887-1915)
THE PERIODIC TABLE
HORIZONTAL ROWS: PERIODS
seven periods 2 to 32 elements in a period properties of the elements change
as you move across a period this pattern repeats from period to
period: The Periodic Law
Elements in a group have similar physical and chemical properties.
Groups identified by A or B and a #Group A are the representative
elementsGroup A can be divided into three
broad classes
VERTICAL COLUMNS: GROUPS/FAMILIES
high electrical conductivityhigh luster when cleanductilemalleable
1. METALS
divided into:alkali metals – group 1Aalkaline earth metals – group 2Atransition metals – group Binner transition metals
1. METALS
poor electrical conductivitynon-lustrousgroup 7A – halogensgroup 8A – noble gases
2. NONMETALS
properties are intermediate between metals and nonmetals
3. METALLOIDS
5.4 The Periodic Table…
1. groups 10. alkaline earth
2. periods metals
3. atomic # 11. group 7A
4. group 12. metalloids
5. rep. elements 13. ST
6. noble gases 14. AT
7. transition metals 15. AT
8. inner tr. metals 16. NT
9. alkali metals
5.4 The Periodic Table…
17. E 25. nonmetals: N, P
18. G metalloids: As, Sb
19. A metal: Bi
20. F 26. malleable, ductile,
21. C conduct electricity, etc.
22. D
23. H
24. B
Mass Defect – missing mass?
• Masses of particles that make up an atom are added, the sum is always larger than the actual mass of the atom.
• The missing mass is the matter converted into energy when the nucleus was formed from its component protons and neutrons.
Mass Defect
• Calculate the mass defect of a chlorine-35 atom.
• The actual mass of chlorine-35 is 5.81 x 10-23 grams
• e = 9.11 x 10-28 g• p = 1.67 x 10-24 g• n = 1.67 x 10-24 g