The Atom and You(What are we made of?)

Page 3

Early Greek Theories• 400 B.C.• Democritus thought matter could not

be divided indefinitely.• Called the smallest particle ‘Atomos’

Democritus

• Atom - Smallest particle of an element that retains the chemical identity of that element

Comparison•World population:

7,000,000,000

•Atoms in Cu penny:29,000,000,000,000,000,000,000

John Dalton• 1800 -Dalton proposed a modern atomic model

based on experimentation not on pure reason.

• All matter is made of atoms.• Atoms of an element are identical.• Atoms of different elements combine

in constant ratios to form compounds.• Atoms are rearranged in reactions.

• His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).

V.Montgomery & R.Smith 6

J.J. Thomson (1897)• Applied electric and magnetic fields to

cathode rays and got particles that shot off.

• These particle were negative, electrons.

• “Plum pudding” model of the atom

Negative particles in a positive matrix.

Ernest Rutherford

Most particles passed through. So, atoms are mostly empty.

Some positive -particles deflected or bounced back!

Thus, a “nucleus” is positive & holds most of an atom’s mass.

Radioactive substance path of invisible

-particles

• Rutherford shot alpha () particles at gold foil.

Lead block

Zinc sulfide screen Thin gold foil

Bohr’s model•Electrons orbit the nucleus in “shells”•Proposed that electrons must have enough energy to keep them in constant motion around the nucleus•Analogous to the motion of the planets orbiting the sun

•The further away, the more energy the electron has

Modern Model – Wave Mechanical Model (Electron Cloud)

• Based on the work of many scientists

• Protons (+) and neutrons (0) are in the nucleus

• Electrons (-) are in an orbital (not an exact location of the electron, it is a probable place that the electron is located.

• The thickest (most dense) part of the cloud is the most probable place of the electron - orbital

Wave Mechanical Model (Electron Cloud)

electron

neutron

proton

Regents Question:

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

Regents Question: One 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.

•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.

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.

Notes Now

• Take out paper.

• Atoms are made of smaller particles.– Protons– Neutrons– Electrons

Subatomic Particles

Symbol Location Charge Mass

electron

proton

neutron

Subatomic Particles

Symbol Location Charge Mass

electron e−

proton p+

neutron n

Subatomic Particles

Symbol Location Charge Mass

electron e− empty space

proton p+ nucleus

neutron n nucleus

Subatomic Particles

Symbol Location Charge Mass

electron e− empty space

−1

proton p+ nucleus +1

neutron n nucleus 0

Subatomic Particles

Symbol Location Charge Mass

electron e− empty space

−10.0005 amu

proton p+ nucleus +1 1 amu

neutron n nucleus 0 1 amu

Regents Question:

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.

Regents Question: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

Regents Question:

Which subatomic particle has no charge?

(1) alpha particle

(2) beta particle

(3) Neutron

(4) electron

Electron Configurations

• Electron Configurations: arrangement of e- in an atom.

• There is a distinct electron configuration for each atom in the ground state.

• It is listed on the Periodic Table.

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

•The valence shell contains 1 electron.

•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.

Regents QuestionWhat 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

Regents Question: 06/02 #31

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

(1) 1

(2) 2

(3) 3

(4) 4

Page 4

1. Find element on the Periodic Table.

2. Use the bolded number for number of electron. This is the Atomic Number.

3. The first shell can only contain 2 electron.

4. The next shells have electrons according to the formula 2n2.

5. Draw the correct number of shells and electrons

Sodium - Na

1. Na is element number 11.

2. The bold number is 11, so the electrons equal 11.

3. First shell has 2.

4. The second has 8, so we need three shells.

5. Draw three circles an add the correct number of electrons.

Complete page 4, numbers 2-5.

Page 5

Notes Now

• Take out paper.

Ions

• When an atom, (neutral), gain or loses and electron it is known as an ION.

• I do not drink GIN.

• It makes my LIPs burn.

•Ion•atom with an electrical charge

•Anion•more electrons than protons: - charge

•Cation•more protons than electrons: + charge

25 Mg2+12

How many electrons, protons and neutrons?

Anion or Cation?

179 Hf 4+ 72

How many electrons, protons and neutrons?

Anion or Cation?

37 Cl−17

How many electrons, protons and neutrons?

Anion or Cation?

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Sodium Ion – Na+1

1. Na is element number 11.

2. The bold number is 11, so the electrons equal 11. Take into account the charge.

3. +1 means one less electron. LIP – losing is positive. First shell has 2.

4. First shell has 2. The second has 8. There is no third shell.

5. Draw two circles an add the correct number of electrons.

Complete page 4, numbers 7-10.

Page 8

Review Time

• Take out paper.

Atomic Particles

• Atomic Number– Number of protons– Number of positive charges– Number of electrons in a neutral atom

• Mass Number– The mass of an atom (amu)

14 N 7

How many electrons, protons and neutrons?

15 N 7

How many electrons, protons and neutrons?

Isotopes

• Atoms of the same element with the same atomic number but different mass number

• Ex. Protium - Hydrogen proton =1 neutron = 0 Deuterium – Hydrogen proton = 1 neutron = 1 Tritium – Hydrogen proton = 1 neutron = 2

Mass numberThe number of protons plus neutrons in an atom

Commonly follows chemical symbol: Ni-59

Iron-56 OR Fe-56

How many electrons, protons and neutrons?

What has 5 protons and 6 neutrons?

Page 11

Regents Question:

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

Regents Question:

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

Regents Question:

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.

Regents Question:

The nucleus of an atom of K-42 contains

(1) 19 protons and 23 neutrons

(2) 19 protons and 42 neutrons

(3) 20 protons and 19 neutrons

(4) 23 protons and 19 neutrons

Regents Question:

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.

Regents Question:

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

Regents Question:

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

(1) Charged atoms

(2) Charged nuclei

(3) Isomers

(4) Isotopes

Take Out Periodic Table

• What is the mass of the following:

H C Cl

Periodic TableShows Atomic Mass

•Atomic Mass•average mass of an element’s atoms averaged according to their relative abundance•sum of relative abundances x isotope mass

WHAT?

Why is:

Atomic mass = 35.453 for Cl?(Shouldn’t it be a whole number?)

All elements have Isotopes

Remember Isotopes Are

• Same element

• Different number of neutrons

• Different Mass Numbers

• Isotopes occur in different amounts

• Remember Carbon Dating from Earth Science?

How do we calculate Atomic Mass?(AKA Average Atomic Mass)

1. Use the Mass number of the Isotopes.2. Multiply that number by the percentage.3. Add the resulting number together.

37 * .25 = 9.2535 * .75 = 26.25

35.5

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

Regents Question:

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

Regents Question:Hydrogen 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

Regents Question:

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.

Page 12

Notes Again

• Take out paper

The Excited State

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

•Change the electron configuration•Normal electron configuration is

•2-8-1•Possible excited states for Na are:

• 2-7-2•1-8-2

How is Sodium excited?

What are possible excited states for the following:

• Hydrogen

• Gold

• Potassium

• Chlorine

• Magnesium

• Manganese

• Flourine

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

Regents Question:

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

Regents Question:

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

Regents Question:Base 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