1 Lecture 2: Atoms and Elements Lecture Outline Defining matter and its types Elements and symbols...

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Lecture 2: Atoms and Elements

Lecture Outline Defining matter and its types Elements and symbols The periodic table The atom Atomic number and mass number Isotopes and atomic mass Electron energy levels Electron configuration Periodic trends

(as in before, group activity takes center and front in the lecture)

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Defining Matter and its types

Matter: Matter is stuff. it is what makes up a substance. Matter makes things we see everyday such as water, wood, cooking pan, clothes, shoes, etc.

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Properties of Matter

Type of Properties

PhysicalObtained without changing identity

(No color, shape, taste, or density change)

ChemicalObtained by changing identity(New color, shape, taste, etc)

Physical ChangeChange without changing identity

and no new substances formed

Chemical ChangeChange in which new substancesare formed by changing identity

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Elements and Symbols

Robert Boyle (1627-1691: Elements are substances that cannot be separated into simpler substances

Robert had no preconceived ideas about how many elements there might be …

Elements are the building blocks of matter

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

gold carbon aluminum

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Number of Elements

Matter is composed of 115 different elements (88 naturally occurring) millions of compounds

In comparison, English language has 26 letters millions of words and sentences

Elements not evenly distributed 9 elements in the earth’s crust make up 98% of the mass Oxygen is the most abundant: 20% of air, almost 50% of earth’s

crust Elements in living matter also not evenly distributed selected for

biological function Oxygen is still most abundant, followed by carbon, hydrogen, and

nitrogen Calcium, phosphorus, magnesium, potassium, sodium, chlorine,

sulfur, and iron are all present in significant amounts

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Element Names

Element named after many things: Places of discovery Planets minerals People (Scientists) Colors Mythology

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Symbols of Elements

Learn the FIRST 20 elements and their names (TEST Material)

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Symbols from Latin Names

Some symbols are derived from Latin names as shownbelow:

Cu, copper (cuprum) Au, gold (aurum)

Fe, iron (ferrum) Ag, silver (argentum)


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The Periodic Table: Groups vs. Periods

• Groups contain elements with similar properties in vertical columns.

• Periods are horizontal rows of elements.

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The Periodic Table

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Group Numbers

Group Numbers Use the letter A for the representative elements (1A to 8A) and

the letter B for the transition elements Also use numbers 1-18 to the columns from left to right Several groups of representative elements have common names


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The heavy zigzag line separates metals and nonmetals Metals are located to the

left Nonmetals are located to

the right. Metalloids are located

along the heavy zigzag line between the metals and nonmetals


Metals, Nonmetals, and Metalloids

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Properties of Metals, Nonmetals, and Metalloids

Metals Are shiny and ductile Are good conductors of heat and electricityNonmetals Are dull, brittle, and poor conductors of heat and

electricity Are good insulatorsMetalloids Are better conductors than nonmetals, but not as good

as metals Are used as semiconductors and insulators

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Pause: ALE 2

Group activity: all groups work on problems on ALE IIB worksheet, problems 3-6

Need volunteers to work on the problems written on the board. If no volunteers immediately, will call names. Everyone will do problems on the board sooner or later

While working on the problems, ask if you have any questions. I’m more than happy to help

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Dalton’s Atomic Theory

Atoms

Are tiny particles of matter

Of an element are similar and different from other elements

Of two or more different elements combine to form compounds

Are rearranged to form new combinations in a chemical reaction


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Subatomic Particles

Atoms contains subatomic particles. Protons have a positive (+) charge. Electrons have a negative (-) charge. Neutrons are neutral Coulomb's law: Like charges repel

and unlike charges attract


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An atom consists

Of a nucleus that contains protons and neutrons

Of electrons in a large, empty space around the nucleus


Structure of the Atom

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Atomic Mass Scale

On the atomic mass scale for subatomic particles 1 atom mass unit (amu) is defined as 1/12 of the mass of

the carbon-12 atom A proton has a mass of about 1 (1.007) amu A neutron has a mass of about 1(1.008) amu An electron has a very small mass, 0.000549 amu

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Atomic Number and Mass Number

The atomic number Is specific for each element and is the same for all atoms

of an element. Is equal to the number of protons in an atom. Appears above the symbol of an element.

• The mass number : represents the number of particles in the nucleus and is equal to sum of protons and neutrons in the nucleus. Number of protons + Number of neutrons

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Na

Atomic Number

Symbol

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Atomic Number and Protons

Examples of atomic number and number of protons:

Hydrogen has atomic number 1, every H atom has one proton.

Carbon has atomic number 6, every C atom has six protons.

Copper has atomic number 29, every Cu atom has 29 protons.

Gold has atomic number 79, every Au atom has 79 protons.

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Number of Electrons in Atom Atoms are neutral In each atom, number of protons is equal to that

of electrons

number of protons = number of electrons

For instance, an aluminum atom has 13 protons and 13 electrons. The net charge is zero

13 protons (13+) + 13 electrons (13 -) = 0

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Isotopes and Isotopic Notation

Isotopes

Elements of same type, same number of protons, but different number of neutrons.

Isotopes have identical properties, mass, and sometimes radioactivity

Nuclear Symbol

atomic number zmass number aX

atomic number 11mass number 23N

a

Example: Sodium atom

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For an atom, the nuclear symbol gives the number of Protons (p+) Neutrons (n) Electrons (e-)

16 31 65

O P Zn 8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n 8 e- 15 e- 30 e-

Nuclear Symbols

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Atomic Mass

The atomic mass of an element

Is listed below the symbol of each element on

the periodic table.

Gives the mass of an “average” atom of each

element compared to 12C.

Is not the same as the mass number

Na22.99

Summary

Atomic mass = average mass of an atom in each element

Mass number = # of protons + # of neutrons in the nucleus

Atomic number = number of protons in an atom

Learning Check

Fill the following table for neutral atoms:

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Element Name

Symbol Atomic Number

Mass Number

Number of

Protons

Number of

Neutrons

Number of Electrons

Boron 10

Cl 35

8 16

92 146

8 6

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Elements and Their Atomic Mass

Most elements have two or more isotopes that contribute to the atomic mass of that element.

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Calculating Average of Masses

To calculate an atomic mass, the contribution of each isotope is determined by multiplying the mass of each isotope by its percent abundance and adding the results

Example: magnesium has three isotopes, Mg-24 (23.99 amu, 78.70%), Mg-25 (24.99 amu, 10.13%) and Mg-26 (25.98 amu, 11.17%). Calculate the atomic mass of magnesium.

Isotope: Mass x Abundance (%) = Contribution to average Mg amu

24Mg25Mg26Mg

23.99

24.99

25.98

78.70/100

10.13/100

11.17/100

Average Atomic Mass:

18.88

2.532

2.902

24.31

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Pause: ALE 2

Group activity: all groups work on problems on ALE 2 worksheet, problems 1and 2, 7-9


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Electron Energy Levels


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Electron Energy Levels

Electrons are arranged in

specific energy levels that Are labeled n = 1, n = 2, n =

3, and so on.

Increase in energy as n increases.

Have the electrons with the lowest energy in the first energy level (n=1)closest to the nucleus.


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Energy Level Changes

An electron absorbs energy to “jump” to a higher energy level.

When an electron falls to a lower energy level, energy is emitted.

In the visible range, the emitted energy appears as a color.


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Energy Emitted


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Sublevels

Sublevels Contain electrons with the same energy. Are found within each energy level. Are designated by the letters s, p, d, f.

The number of sublevels is equal to the value of the principal quantum number (n).

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Number of Sublevels


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Energy of Sublevels

In any energy level, The s sublevel has the lowest energy. The s sublevel is followed by the p, d, and f sublevels

in order of increasing energy. Higher sublevels are possible, but only s, p, d, and f

sublevels are needed to hold the electrons in the atoms known today.

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Orbitals

An orbital Is a three- dimensional space

around a nucleus where an electron is most likely to be found.

Has a shape that represents electron density (not a path the electron follows).

Can hold up to 2 electrons. Contains two electrons that must

spin in opposite directions.


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s Orbitals

An s orbital Has a spherical shape

around the nucleus. Increases in size around the

nucleus as the energy level n value increases.

Is a single orbital found in each s sublevel.


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p Orbitals

A p orbital Has a two-lobed shape. Is one of three p orbitals that make up each p

sublevel. Increases in size as the value of n increases.


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Sublevels and Orbitals

Each sublevel consists of a specific number oforbitals. An s sublevel contains one s orbital. A p sublevel contains three p orbitals. A d sublevel contains five d orbitals. An f sublevel contains seven f orbitals.


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Electrons in Each Sublevel

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Pause: ALE 2

Group activity: all groups work on problems on ALE 2 worksheet, problems 11 and 12



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Electron Configurations


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Energy levels are filled with electrons In order of increasing energy. Beginning with quantum number n = 1. Beginning with s followed by p, d, and f.

Order of Filling

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Energy Diagram for Sublevels


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An orbital diagram shows Orbitals as boxes in each sublevel. Electrons in orbitals as vertical arrows. Electrons in the same orbital with opposite spins (up

and down vertical arrows).

Orbital diagram for Li

1s2 2s1 2p filled half-filled empty

Orbital Diagrams

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Order of Filling

Electrons in an atom Fill orbitals in sublevels of the same type with

one electron until half full, Then pair up in the orbitals using opposite spins.


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Writing Orbital Diagrams

The orbital diagram

for carbon consists of Two electrons in the 1s

orbital. Two electrons in the 2s

orbital. One electron each in

two of the 2p orbitals


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Write the orbital diagrams for

A. Nitrogen

B. oxygen

C. magnesium

Individual Learning Check

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An electron configuration Lists the sublevels filling with electrons in order of

increasing energy. Uses superscripts to show the number of electrons

in each sublevel. For neon (10 electrons) is as follows:

number of electrons

sublevel 1s2 2s2 2p6

Electron Configuration

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Example: Period 1 Configurations

In Period 1, the first two electrons enter the 1s orbital

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Abbreviated Configurations

An abbreviated configuration shows The symbol of the noble gas in brackets that

represents completed sublevels. The remaining electrons in order of their sublevels,

Example: Chlorine has a configuration of

1s2 2s2 2p6 3s2 3p5

[Ne]

The abbreviated configuration for chlorine is

[Ne] 3s2 3p5

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Period 2 Configurations


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A. The correct electron configuration for nitrogen is 1) 1s2 2p5 2) 1s2 2s2 2p6 3) 1s2 2s2 2p3

B. The correct electron configuration for oxygen is 1) 1s2 2p6 2) 1s2 2s2 2p4 3) 1s2 2s2 2p6

C. The correct electron configuration for calcium is1) 1s2 2s2 2p6 3s2 3p6 3d2

2) 1s2 2s2 2p6 3s2 3p6 4s2

3) 1s2 2s2 2p6 3s2 3p8

TAPPS Learning Check

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Write the electron configuration and abbreviated configuration for each of the following elements:

A. Cl

B. S

C. K

TAPPS Learning Check

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Sublevel Blocks on the Periodic TableThe periodic table consists of sublevel blocks arranged in order of increasing energy.

Groups 1A-2A = s level Groups 3A-8A = p level Groups 3B to 2B = d level Lanthanides/Actinides = f level

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Sublevel Blocks



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Using the periodic table, write the electron configuration for silicon.

SolutionSilicon is in group 4A, period 3, thus we would stop at

3p and it would have 2 electrons in the 3p orbital:

all the sublevel blocks in order gives:

1s2 2s2 2p63s2 3p2

Writing Electron Configurations

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The 4s orbital has a lower energy than the 3d orbitals.

In potassium K, the last electron enters the 4s orbital instead of the 3d

1s 2s 2p 3s 3p 3d 4s

Ar 1s2 2s2 2p63s2 3p6

K 1s2 2s2 2p63s2 3p64s1

Ca 1s2 2s2 2p63s2 3p64s2

Sc 1s2 2s2 2p63s2 3p6 3d1 4s2

Ti 1s2 2s2 2p63s2 3p6 3d2 4s2

Electron Configurations d Sublevel

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Exceptions in Sublevel Block Order

Within the filling of the 3d sublevel, exceptions occur for chromium and copper Both Cr and Cu, in the 3d sublevel, are close

to either a half-filled or filled sublevel Cr has only 1 electron in the 4s and 5 e-s in

the 3d sublevel …half-filled 3d, added stability Cu has 1 e- in 4s and 10 e-s in 3d sublevel …

completely filled 3d, stable After 4s and 3d, 4p is filled

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Using the periodic table, write the electron configuration for manganese.

Solution1s2 2s2 2p63s2 3p6 4s2 3d5

Writing Electron Configurations

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A. The last two sublevel blocks in the electron configuration for Co are

1) 3p64s2

2) 4s24d7 3) 4s23d7

B. The last three sublevel blocks in the electron configuration for Sn are

1) 5s25p24d10

2) 5s24d105p2

3) 5s25d105p2

Learning Check

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Learning Check

Give the symbol of the element that has

A. [Ar]4s2 3d6

B. Four 3p electrons

C. Two electrons in the 4d sublevel

D. The element that has the electron configuration

1s2 2s2 2p6 3s2 3p6 4s2 3d2

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Pause: ALE 2

Group activity: all groups work on problems on ALE 2 worksheet, problems 12-15



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Periodic Trends


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Valence Electrons

The valence electrons Determine the chemical properties of the elements. Are the electrons in the highest energy level. Are related to the Group number of the element.

Example: Phosphorus has 5 valence electrons 5 valence electrons

P Group 5A(15) 1s2 2s2 2p6 3s2 3p3

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All the elements in a group have the same number of

valence electrons.

Example: Elements in Group 2A(2) have two (2) valence electrons.

Be 1s2 2s2

Mg 1s2 2s2 2p6 3s2

Ca [Ar] 4s2

Sr [Kr] 5s2

Groups and Valence Electrons

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Periodic Table and Valence Electrons

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Electron-Dot Symbols

An electron-dot symbol Indicates valence electrons

as dots around the symbol of the element.

Of Mg shows two valence electrons as single dots on the sides of the symbol Mg.

. .· Mg · or Mg · or · Mg or ·

Mg

· Electron-dot symbolCopyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Writing Electron-Dot Symbols

The electron-dot symbols for Groups 1A(1) to 4A(14) use single dots.

· · Na · · Mg · · Al · · C ·

· Groups 5A(15) to 7A(17) use pairs and single dots.

· · · · · P · : O · · ·

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State the number of valence electrons for each:A. O

1) 4 2) 6 3) 8

B. Al

1) 13 2) 3 3) 1

C. Cl

1) 2 2) 5 3) 7

Learning Check

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State the number of valence electrons for each.

A. 1s2 2s2 2p6 3s2 3p1

B. 1s2 2s2 2p6 3s2

C. 1s2 2s2 2p5

Learning Check

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Groups and Electron-Dot Symbols

In a group, all the electron-dot symbols have the same number of valence electrons (dots).

Example: Atoms of elements in Group 2A(2) each have 2 valence electrons.

2A(2)· Be ·

· Mg ·

· Ca ·

· Sr ·

· Ba ·

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A. X is the electron-dot symbol for

1) Na 2) K 3) Al

B. X is the electron-dot symbol of

1) B 2) N 3) P

Learning Check

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Atomic Size

Atomic size is Described using

the atomic radius. The distance from

the nucleus to the

valence electrons.


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Atomic Radius Within A Group

Atomic radius Increases going

down each group of representative elements.

Decreases going across each period.


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Ionization Energy

Ionization energy Is the energy it takes to remove a valence electron.

Na(g) + Energy (ionization) Na+(g) + e-

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Ionization Energy

The ionization

energies of

Metals are low

Nonmetals are high


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Pause: Group Work

Do all the problems in group activity 2 as group

1 Lecture 2: Atoms and Elements Lecture Outline Defining matter and its types Elements and symbols...

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