Atomic StructureAtomic StructureDistinguishing Among AtomsDistinguishing Among Atoms

Prentice-Hall Chapter 4.3Prentice-Hall Chapter 4.3Dr. YagerDr. Yager

ObjectivesObjectives

ExplainExplain what makes elements and isotopes what makes elements and isotopes different from each other.different from each other.

CalculateCalculate the number of neutrons in an the number of neutrons in an atom.atom.

CalculateCalculate the atomic mass of an element. the atomic mass of an element.

ExplainExplain why chemists use the periodic table. why chemists use the periodic table.

Elements are different because they Elements are different because they contain different numbers of protons.contain different numbers of protons.

TheThe atomic numberatomic number of an element is the of an element is the number of protons in the nucleus of an number of protons in the nucleus of an atom of that element.atom of that element.

Note: Electrons equal the number of

protons in a neutral atom

19 5

16

B 5

16

23 23

The total number of protons and neutrons in The total number of protons and neutrons in an atom is called the an atom is called the mass numbermass number..

The number of neutrons in an atom is the The number of neutrons in an atom is the difference between the mass number and difference between the mass number and atomic number.atomic number.

Au is the chemical symbol for gold.Au is the chemical symbol for gold.

Mass Number

Atomic Number

Mini-QuizMini-Quiz

IsotopesIsotopes

IsotopesIsotopes are atoms that have the same are atoms that have the same number of protons but different numbers of number of protons but different numbers of neutrons. neutrons.

Because isotopes of an element have different Because isotopes of an element have different numbers of neutrons, they also have different numbers of neutrons, they also have different mass numbers.mass numbers.

Despite these differences, isotopes are chemically Despite these differences, isotopes are chemically alike because they have identical numbers of alike because they have identical numbers of protons and electrons.protons and electrons.

Mini-QuizMini-Quiz

CrCrCr 5324

5224

5024

Atomic MassAtomic Mass

It is useful to compare the relative masses of It is useful to compare the relative masses of atoms to a standard reference isotope. atoms to a standard reference isotope. Carbon-12 is the standard reference isotope. Carbon-12 is the standard reference isotope.

Carbon-12 has a mass of exactly 12 atomic Carbon-12 has a mass of exactly 12 atomic mass units. mass units.

An An atomic mass unit (amu)atomic mass unit (amu) is defined as is defined as exactly one twelfth of the mass of a carbon-exactly one twelfth of the mass of a carbon-12 atom.12 atom.

Atomic MassAtomic Mass

The The atomic massatomic mass of an element is a of an element is a weighted average massweighted average mass of the atoms in a of the atoms in a naturally occurring sample of the element.naturally occurring sample of the element.

A weighted average mass reflects both the A weighted average mass reflects both the mass and the relative abundance of the mass and the relative abundance of the isotopes as they occur in nature.isotopes as they occur in nature.

Weighted Average Mass of a Chlorine Atom

The atomic mass of copper is 63.546 The atomic mass of copper is 63.546 amu. Which isotope is more abundant, amu. Which isotope is more abundant, Copper-63 or Copper-65?Copper-63 or Copper-65?

Calculating the Relative Calculating the Relative Abundance of CuAbundance of Cu

62.9 62.9 amuamu (x) + 64.9 (x) + 64.9 amuamu (1- x) = 63.546 (1- x) = 63.546 amuamu

x = 69.2%x = 69.2%

1- x = 30.8%1- x = 30.8%

1. Isotopes of an element have1. Isotopes of an element have

a)a) the same mass number.the same mass number.

b)b) different atomic numbers.different atomic numbers.

c)c) the same number of protons but the same number of protons but different numbers of neutrons.different numbers of neutrons.

d)d) the same number of protons but the same number of protons but different numbers of electrons.different numbers of electrons.

1. Isotopes of an element have1. Isotopes of an element have

a)a) the same mass number.the same mass number.

b)b) different atomic numbers.different atomic numbers.

c)c) the same number of protons but the same number of protons but different numbers of neutrons.different numbers of neutrons.

d)d) the same number of protons but the same number of protons but different numbers of electrons.different numbers of electrons.

2. How many neutrons are in sulfur-33?2. How many neutrons are in sulfur-33?

a)a) 16 neutrons16 neutrons

b)b) 33 neutrons33 neutrons

c)c) 17 neutrons17 neutrons

d)d) 32.06 neutrons 32.06 neutrons

2. How many neutrons are in sulfur-33?2. How many neutrons are in sulfur-33?

a)a) 16 neutrons16 neutrons

b)b) 33 neutrons33 neutrons

c)c) 17 neutrons17 neutrons

d)d) 32.06 neutrons 32.06 neutrons

3. If sulfur contained 90.0% sulfur-32 and 3. If sulfur contained 90.0% sulfur-32 and 10.0% sulfur-34, its atomic mass would 10.0% sulfur-34, its atomic mass would bebe

a)a) 32.2 amu.32.2 amu.

b)b) 32.4 amu.32.4 amu.

c)c) 33.0 amu.33.0 amu.

d)d) 35.4 amu.35.4 amu.

3. If sulfur contained 90.0% sulfur-32 and 3. If sulfur contained 90.0% sulfur-32 and 10.0% sulfur-34, its atomic mass would 10.0% sulfur-34, its atomic mass would bebe

a)a) 32.2 amu.32.2 amu.

b)b) 32.4 amu.32.4 amu.

c)c) 33.0 amu.33.0 amu.

d)d) 35.4 amu.35.4 amu.

Mass SpectrometerMass Spectrometer

Mass SpectrometerMass Spectrometer

Mass SpectrometerMass Spectrometer

The Mass Spectrum for Boron

With 123 atoms of Boron: 23 are Boron-10 and 100 are Boron-11

The total mass is (23 x 10) + (100 x 11) = 1330 amu

The average mass is 1330 / 123 = 10.8 amu

Therefore the atomic mass is 10.8 amu

The Mass Spectrum for The Mass Spectrum for Zirconium (Zr)Zirconium (Zr)

Isotopes of ZrIsotopes of ZrZr-90 51.5%Zr-90 51.5%

Zr-91 11.2%Zr-91 11.2%

Zr-92 17.1%Zr-92 17.1%

Zr-94 17.4%Zr-94 17.4%

Zr-96 2.8%Zr-96 2.8%

Atomic Mass = 0.515(90) + 0.112(91) + 0.171(92) + 0.174(94) + 0.028(96)

Periodic TablePeriodic Table

A A periodic tableperiodic table is an arrangement of is an arrangement of elements in which the elements are elements in which the elements are separated into groups based on a set of separated into groups based on a set of repeating properties. repeating properties.

A periodic table allows you to easily compare A periodic table allows you to easily compare the properties of one element (or a group of the properties of one element (or a group of elements) to another element (or group of elements) to another element (or group of elements).elements).

Periodic TablePeriodic Table

PeriodPeriod

Each horizontal row of the periodic table is Each horizontal row of the periodic table is called acalled a periodperiod..

Within a given period, the properties of the Within a given period, the properties of the elements vary as you move across it from elements vary as you move across it from element to element.element to element.

A PeriodA Period

GroupGroup

Each vertical column of the periodic table Each vertical column of the periodic table is called a is called a groupgroup, or family., or family.

Elements within a group have similar Elements within a group have similar chemical and physical properties.chemical and physical properties.

A GroupA Group