Distinguishing Between Atoms

1
Distinguishing Between Atoms

• Atomic Number equals the number of protons in
  the nucleus of an atom of that element
• Atoms are electrically neutral, therefore the
  number of electrons must equal the number of
  protons
• How is the number of electrons for a neutral atom
  of a given element related to the atomic number
  of that element?
• The atomic number is equal to the number of
  electrons

2
Atoms of the First Ten Elements Atoms of the First Ten Elements Atoms of the First Ten Elements Atoms of the First Ten Elements Atoms of the First Ten Elements Atoms of the First Ten Elements Atoms of the First Ten Elements
Name Symbol Atomic Number Name Symbol Atomic Number Name Symbol Atomic Number Composition of the Nucleus Composition of the Nucleus Mass Number Number of electrons Mass Number Number of electrons
Name Symbol Atomic Number Name Symbol Atomic Number Name Symbol Atomic Number Protons Neutrons Protons Neutrons Mass Number Number of electrons Mass Number Number of electrons
Hydrogen H 1 1 0 1 1
Helium He 2 2 2 4 2
Lithium Li 3 3 4 7 3
Beryllium Be 4 4 5 9 4
Boron B 5 5 6 11 5
Carbon C 6 6 6 12 6
Nitrogen N 7 7 7 14 7
Oxygen O 8 8 8 16 8
Fluorine F 9 9 10 19 9
Neon Ne 10 10 10 20 10
3
Element block
4
Review

• 7
• 7, number of protons equals the number of
  electrons

• The element Nitrogen has an atomic number of
  what?
• How many protons and how many electrons are in a
  neutral nitrogen atom?

5
How many protons and electrons are in each of the
following atoms?

• Calcium
• 19,19
• 19,20
• 20,20
• 20,19

• Fluorine
• 9,8
• 9,9
• 8,9
• 8,8
• Aluminum
• 12,13
• 12,12
• 13,12
• 13,13

6
Complete the Table
Element Atomic Number Protons Electrons
K 19 19
5
16
23
7
Mass Number the total number of protons and
neutrons in an atom

• Mass protons neutrons
• Example Oxygen
• 16 8 n
• n 8

8
The following is shorthand for writing the of
protons and neutrons, you dont need to write the
of electrons because they are the same as the
of protons

• The large "X" represents where you will find
  the atom's elemental symbol.  The mass number,
  which is given the symbol "A", is located in the
  upper left-hand corner.  The atomic number (also
  called nuclear charge), which is given the symbol
  "Z", is found in the lower left-hand corner.

Number of neutrons    mass number  -  atomic
number
9
Number of neutrons    mass number  -  atomic
number

• In the case of neon (Ne)
• Number of neutrons    20- 10 10

• In the case of carbon (C)
• Number of neutrons    12- 6 6

10
More Examples
Elemental Symbol
of Protons (equal to Z) 3 9
of Neutrons(equal to A-Z) 4 10
of electrons (equal to Z modified by charge number) 3 9
11
How many protons, electrons, and neutrons are in
the following atoms?
Atomic Number Mass Number
(a) Beryllium (Be) 4 9
(b) Neon (Ne) 10 20
(a) Sodium (Na) 11 23
12
How many neutrons are in each atom?

• 16 O
• 8
• 8
• 16
• 24

• 32 S
• 16
• 32
• 48
• 16

13
Express the composition of the following atom in
shorthand form

• Carbon-12
• 12 C
• 6
• 6 C
• 12
• 18 C
• 12

• Fluorine-19
• 9 F
• 19
• 28 F
• 9
• 28 F
• 19
• 19 F
• 9

14
Isotopes atoms that have the same number of
protons but different numbers of neutrons

• Isotopes have different mass numbers because they
  have different numbers of neutrons
• They are chemically alike because they have
  identical numbers of protons electrons, which
  are the subatomic particles responsible for
  chemical behavior.

15
Example Hydrogen has three isotopes each
isotope has 1 proton in its nucleus.
16
Two isotopes of carbon are carbon 12 and carbon
13. Write the symbol for each isotope using
superscripts and subscripts to represent mass
and atomic number

• Carbon-12
  Carbon-13
• ___
  ___
• ___C
  ___C

17
Determine the number of protons, neutrons, and
electrons for each of the following isotopes of
Neon

• Neon-20
• 22
• 10
• 11
• Neon-21
• 21
• 10
• 11

• Neon-22
• 22
• 10
• 12

18
Atomic Mass
Properties of Subatomic Particles Properties of Subatomic Particles Properties of Subatomic Particles Properties of Subatomic Particles Properties of Subatomic Particles
Particle Symbol Relative electrical charge Relative mass (Mass of proton 1) Actual mass (g)
Electron e- 1- 1/1840 9.11x10-28
Proton P 1 1 1.67x10-24
Neutron n? 0 1 1.67x10-24
Actual mass of a proton or a neutron is very
small (1.67 x10-24 g) Since about the 1920s, it
has been possible to determine these masses
(protons neutrons) by using a mass spectrometer
19

• This is impractical to work with, so a reference
  isotope as a standard is used. The chosen isotope
  is C-12. It was assigned a mass of EXACTLY 12
  atomic mass units or amu
• Carbon-12 has 6 protons and 6 neutrons, making up
  its mass
• Since the mass of an atom mainly depends on the
  number of protons and neutrons, shouldnt the
  atomic mass of an element be a whole number?
  Thats usually not the case, Cl is 35.453 amu
• The reason for this involves the relative
  abundance of the naturally occurring isotopes of
  the element. Most occur as a mixture of two or
  more isotopes
• Each isotope has a fixed mass and a natural
  percent abundance

20
The atomic mass is a weighted average of all
naturally occurring isotopes

• http//www.sisweb.com/referenc/source/exactmaa.htm
  

21

• Example Chlorine
• 35 Cl and 37 Cl
• 17 17
• 76 24
• Three more 35 Cl for every one 37 Cl
• 17
  17
• (Remember the of protons and neutrons atomic
  mass)
• abundance
• of protons 17 17 17 17 68
• of neutrons 18 18 18 20 74
• 68 74 35.5 amu
• 4

Therefore, the Atomic Mass is a weighted average
mass of the atoms in a naturally occurring sample
of the element
22
Review

• Which isotope of copper is more abundant copper
  63 or copper 65?
• (the atomic mass of copper is 63.546 amu)
• Copper-63
• Boron has two isotopes boron-10 and boron-11,
  which is more abundant
• (atomic mass is 10.81 amu)?
• Boron -11

23

• Element X has two natural isotopes. The isotope
  with a mass of 10.012 amu (10X) has a relative
  abundance of 19.91. The isotope with a mass of
  11.009 amu (11X) has a relative abundance of
  80.09. Calculate the atomic mass of this
  element.
• 10X 10.012 x 0.1991 1.993 amu
• 11X 11.009 x 0.8009 8.817 amu
• 10.810
  amu
• What is this element?
• Boron

24

• Calculate the atomic mass of Bromine. The two
  isotopes of bromine have atomic masses and
  relative abundances of 78.92 amu (50.69) and
  80.92 amu (49.31)
• 79.91 amu