1 the physical setting chemistry 2 i. atomic concepts

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The Physical SettingChemistry

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I. Atomic Concepts

J Deutsch 2003 3

The modern model of the atom has evolved over a long period of time through the work of many scientists.

Democritus – matter is made up of particles called atoms Dalton – atoms of the same element are alike – solid

indivisible spheres Thomson – discovers electrons – plum pudding model Rutherford – gold foil experiment – discovers heavy, +

charge nucleus – mostly empty space Bohr – electrons orbit the nucleus

J Deutsch 2003 4

Regents Question: 08/02 #1

Subatomic particles can usually pass undeflected

through an atom because the volume of an atom

is composed of

(1) an uncharged nucleus

(2) largely empty space

(3) neutrons

(4) protons

J Deutsch 2003 5

Regents Question: 01/03 #62-64One model of the atom states that atoms are tiny particles composed of a uniform mixture of positive and negative charges. Scientists conducted an experiment where alpha particles were aimed at a thin layer of gold atoms.

Most of the alpha particles passed directly through the gold atoms. A few alpha particles were deflected from their straight-line paths. An illustration of the experiment is

shown below.

J Deutsch 2003 6

Regents Question cont’d

•Most of the alpha particles passed directly through the gold atoms undisturbed. What does this evidence suggest about the structure of the gold atoms?

•A few of the alpha particles were deflected. What does this evidence suggest about the structure of the gold atoms?

•How should the original model be revised based on the results of this experiment?

Most of the atom is empty space.

There is central + charge. The nucleus is +.

The atom is not a uniform mixture of + and - charge. Positive charge is located in a heavy central mass.

J Deutsch 2003 7

Regents Question: 06/03 #67John Dalton was an English scientist who proposed that atoms were hard, indivisible spheres. In the modern model, the atom has a different internal structure.

•Identify one experiment that led scientists to develop the modern model of the atom.

Rutherford’s gold foil experiment

J Deutsch 2003 8

Regents Question cont’dJohn Dalton was an English scientist who proposed that atoms were hard, indivisible spheres. In the modern model, the atom has a different internal structure.

•Describe this experiment.

•State one conclusion about the internal structure of the atom, based on this experiment.Most of the atom is empty space.

Rutherford’s shot alpha particles a piece of gold foil. Most of the alpha particles went through, some were deflected and some were reflected.

J Deutsch 2003 9

In the wave-mechanical model (electron cloud model), the electrons are in orbitals, which are defined as the regions of the most probable electron location (ground state).

An orbital is the area of highest probability of finding an electron.

J Deutsch 2003 10

Regents Question: 06/03 # 5

The region that is the most probable location of an electron in an atom is

(1) the nucleus

(2) an orbital

(3) the excited state

(4) an ion

J Deutsch 2003 11

Regents Question: 06/02 #2The modern model of the atom shows that electrons are

(1) orbiting the nucleus in fixed paths

(2) found in regions called orbitals

(3) combined with neutrons in the nucleus

(4) located in a solid sphere covering the nucleus

J Deutsch 2003 12

Each atom has a nucleus, with an overall positive charge, surrounded by one or more negatively charged electrons.

J Deutsch 2003 13

The proton is positively charged, and the neutron has no charge. The electron is negatively charged.

Charge

Mass

J Deutsch 2003 14

The mass of each proton and each neutron is approximately equal to one atomic mass unit. An electron is much less massive than a proton or a neutron.

Charge

Mass

J Deutsch 2003 15


Which subatomic particle has no charge?

(1) alpha particle

(2) beta particle

(3) Neutron

(4) electron

J Deutsch 2003 16

Subatomic particles contained in the nucleus include protons and neutrons.

Particles in the nucleus (protons and neutrons) are called nucleons

The mass of the atoms is concentrated in the nucleus

Electrons are not found in the nucleus, they orbit the nucleus.

The net charge of the nucleus is positive (+)

J Deutsch 2003 17


Which statement best describes electrons?

(1) They are positive subatomic particles and are found in the nucleus.

(2) They are positive subatomic particles and are found surrounding the nucleus.

(3) They are negative subatomic particles and are found in the nucleus.

(4) They are negative subatomic particles and are found surrounding the nucleus.

J Deutsch 2003 18

Regents Question: 06/02 #58-60

In the modern model of the atom, each atom is composed of three major subatomic (or fundamental) particles.

• Name the subatomic particles contained in the nucleus of the atom.

• State the charge associated with each type of subatomic particle contained in the nucleus of the atom.

• What is the net charge of the nucleus?

Proton and neutron

Proton is positive and the neutron is neutral

Positive

J Deutsch 2003 19

Protons and electrons have equal but opposite charges. The number of protons equals the number of electrons in an atom.

# of protons = # of electrons

Therefore, atoms are electrically neutral.

J Deutsch 2003 20

Atomic Mass-number of nucleons (protons + neutrons)

Atomic number # of protons in the nucleus.

# neutrons = mass # - atomic #

J Deutsch 2003 21

The atomic number for an element cannot change but its mass number can.

Atomic Number – The number of protons in the nucleus of an atom– Determines which element

Mass Number– The number of nucleons (protons + neutrons)

# neutrons = mass # - atomic #

J Deutsch 2003 22


In which list are the elements arranged in order of increasing atomic mass?

(1) Cl, K, Ar

(2) Fe, Co, Ni

(3) Te, I Xe

(4) Ne, F, Na

Look for the masses on the periodic table of the elements.

J Deutsch 2003 23


The number of neutrons in the nucleus of an atom can be determined by

(1) Adding the atomic number to the mass number

(2) Subtracting the atomic number from the mass number

(3) Adding the mass number to the atomic mass

(4) Subtracting the mass number from the atomic number

J Deutsch 2003 24


The atomic number of an atom is always equal to the number of its

(1) protons, only

(2) neutrons, only

(3) protons plus neutrons

(4) protons plus electrons

J Deutsch 2003 25


The nucleus of an atom of K-42 contains

(1) 19 protons and 23 neutrons




J Deutsch 2003 26


What is the total number of protons in the

nucleus of an atom of potassium-42?

(1) 15

(2) 19

(3) 39

(4) 42

The mass number (42) is not necessary to find the number of protons.

J Deutsch 2003 27

Electron Configuration tells us how many electrons in each principal energy level (shell).

Atomic Number = 7 Mass Number = 14

7 protons 7 neutrons 7 electrons Electron

configuration: 2-5

J Deutsch 2003 28

The electron configuration for the ground state of an atom is given on the Periodic Table of the Elements.

Electron Configuration

J Deutsch 2003 29

Each electron in an atom has its own distinct amount of energy.

When electrons are in their lowest energy state, it is called the ground state

The ground state for Na is 2-8-1

J Deutsch 2003 30

The maximum number of electrons in a principal energy level (shell) is 2n2.

Energy level (n)

Maximum number of electrons (2n2)

1 2

2 8

3 18

4 32

J Deutsch 2003 31


What is the electron configuration of a sulfur atom in the ground state?

(1) 2-4

(2) 2-6

(3) 2-8-4

(4) 2-8-6

Look at the Periodic Table of the Elements

If you do not know the symbol for sulfur, check Table S

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If an atom gains or loses electrons it is called an ion.

Calcium loses 2 electrons it becomes Ca+2 ion

Flourine gains one electron it becomes F-1

Gaining is negative Losing is positive GIN LIP

J Deutsch 2003 33

When an electron in an atom gains a specific amount of energy, the electron is at a higher energy state (excited state).

Possible excited states for Na are:

2-7-2

1-8-2

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When an electron returns from a higher energy state to a lower energy state, a specific amount of energy is emitted. This emitted energy can be used to identify an element. Emission Spectrum

J Deutsch 2003 35


During a flame test, ions of a specific metal are heated in the flam of a gas burner. A characteristic color of light was emitted by these ions in the flame when the electrons

(1) Gain energy as they return to lower energy levels

(2) Gain energy as they move to higher energy levels

(3) Emit energy as they return to lower energy levels

(4) Emit energy as they move to higher energy levels

J Deutsch 2003 36


When the electrons of an excited atom return to a lower energy state, the energy emitted can result in the production of

(1)alpha particles

(2) Isotopes

(3) protons

(4) spectra

J Deutsch 2003 37

The outermost electrons in an atom are called the valence electrons. In general, the number of valence electrons affects the chemical properties of an element.

The ground state for Na is 2-8-1•The valence shell is the third shell.

•The valence shell contains 1 electron.

J Deutsch 2003 38

Regents Question: 06/03 #51-52Base your answers to the next two questions on

the electron configuration table shown below.

• What is the total number of valence electrons in an atom of electron configuration X?

• Which electron configuration represents the excited state of a calcium atom?

Element Electron Configuration

X 2 –8 –8 –2 Y 2 –8 –7 –3 Z 2 –8 –8

2

2-8-7-3

J Deutsch 2003 39

Regents Question: 08/02 #2What is the total number of electrons in the

valence shell of an atom of aluminum in the

ground state?

(1)8

(2)2

(3)3

(4) 10

J Deutsch 2003 40


In which shell are the valence electrons of the elements in Period 2 found?

(1) 1

(2) 2

(3) 3

(4) 4

J Deutsch 2003 41

Atoms of an element that contain the same number of protons but a different number of neutrons are called isotopes of that element.

Isotopes of Hydrogen

1H – protium 1 proton 0 neutron

2H – deuterium 1 proton 1 neutron

3H – tritium 1 proton 2 neutrons

J Deutsch 2003 42


An atom of carbon-12 and an atom of carbon-14 differ in

(1) Atomic number

(2) Atomic mass

(3) Nuclear charge

(4) Number of electrons

Carbon-12 and carbon-14 are isotopes.

J Deutsch 2003 43


All the isotopes of a given atom have

(1) the same mass number and same atomic number

(2) the same mass number but different atomic numbers

(3) different mass numbers but the same atomic number

(4) different mass numbers and different atomic number

J Deutsch 2003 44


Atoms of the same element that have different numbers of neutrons are classified as

(1) Charged atoms

(2) Charged nuclei

(3) Isomers

(4) Isotopes

J Deutsch 2003 45

The average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes.

Isotope Mass Abundance Calculation12C 12 98.89% 12 x .9889 = 11.87

13C 13 1.108% 13 x 0.01108 = 0.1440

Atomic Mass (weighted average)

12.01 amu

J Deutsch 2003 46


The atomic mass of an element is calculated using the

(1) atomic number and the ratios of its naturally occurring isotopes

(2) atomic number and the half-lives of each of its isotopes

(3) masses and the ratios of its naturally occurring isotopes

(4) masses and the half-lives of each of its isotopes

J Deutsch 2003 47

Regents Question: 01/03 #36Hydrogen has three isotopes with mass numbers of 1, 2,

and 3 and has an average atomic mass of 1.00794 amu. This information indicates that

(1) Equal number of each isotope are present

(2) More isotopes have an atomic mass of 2 or 3 than 1

(3) More isotopes have an atomic mass of 1 rather than 2 of 3

(4) Isotopes have only an atomic mass of 1

1 the physical setting chemistry 2 i. atomic concepts

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