Atoms Bettelheim, Brown, Campbell and Farrell Chapter 2

Atoms

Bettelheim, Brown, Campbell and Farrell

Chapter 2

Classification of MatterMatter

anything that occupies space and has mass

Pure substancesfixed composition; cannot

be further purified

Mixturesa combination of two

or more pure substances

Physicallyseparable into

Elementscannot be

subdivided by chemical or

physical means

Compoundselements unitedin fixed ratios

Homogenous matter

uniform compositionthroughout

Heterogenous matter

nonuniformcomposition

Combine chemically

to form

Classification of Matter

• Element:Element: Pure substance made up of “identical” atoms– 116 known elements

– 88 occur in nature; others man-made

– Represented by one or two letter symbols

– First letter CAPITALIZED; second letter small

Elements found in Nature

• Monatomic elements:Monatomic elements: – Exist as single atoms

• Diatomic elements:Diatomic elements: – Occur as diatomic molecules (pairs of atoms)

– H2, N2, O2, F2, Cl2, Br2, and I2

• Polyatomic elements:Polyatomic elements: – Have three or more atoms per molecule

– O3, P4, S8, diamond


• Compound:Compound: Pure substance made up of two or more elements in a fixed ratio by mass

• Formula of a compound:Formula of a compound: Gives the ratio of each element (uses atomic symbols).– Examples: NaCl H2O


• Mixture:Mixture: Combination of two or more pure substances– Substances may be present in any mass ratio– Each substance has a different set of physical

properties– Each substance keeps its own properties and

identity– Can separate mixture into the individual

substances by using the physical properties of the individual substances in the mixture

Types of Mixtures

• Heterogeneous mixture: Substances are not evenly distributed throughout

• Homogeneous mixture (Solution): Substances are evenly distributed throughout.

Dalton’s Atomic Theory - 1805

• All matter is composed of very tiny particles (atoms)

• All atoms of the same element are the same (same chemical properties)

• Compounds are formed by the chemical combination of two or more different kinds of atoms

• A molecule is a tightly bound combination of two or more atoms that acts as a unit

Evidence for Dalton’s Theory

• Law of Conservation of Mass– Mass can be neither created or destroyed

• Law of Constant Composition– Compounds have a definite composition by mass

OPb PbO C OOC

Carbonmonoxide

Leadoxide

Carbon dioxide

Lead

+ +

.

Subatomic Particles

• The unit of mass is the atomic mass unit atomic mass unit (amu)(amu)– one amu is defined as one-twelfth the mass of an

atom of carbon with 6 protons and 6 neutrons in its nucleus

1 amu = 1.6605 x 10-24 g

Subatomicparticle

Mass(g)Charge

Location in an atom

Proton

Electron

Neutron

1.6726 x 10-24

9.1094 x 10-28

1.6749 x 10-24

1

0.0005

1

+1-1

0

In the nucleus

Outside the ucleus

In the nucleus

1.0073

1.00875.4858 x 10-4

Mass (amu)

Mass (amu);to onesignificantfigure

A typical atom

10-15 m

Neutron

Proton

Nucleus (protons and neutrons)

Space occupied by electrons

10-10 m

Mass and Atomic Numbers

• Mass number:Mass number: Sum of the number of protons plus neutrons in the nucleus of an atom

• Atomic number:Atomic number: Number of protons in the nucleus of an atom

• Notation for single atom or isotope

Mass number (number of protons + neutrons)Atomic number (number of protons) 6C12

Isotopes• Isotopes:Isotopes: atoms with the same number of

protons but a different number of neutrons

• Most elements found as mixtures of isotopes

• Atomic weight: weighted average of masses of isotopes of an element

C136C12

6 C146

75.77100

x 34.97 amu + 24.23100

x 36.97 amu = 35.45 amu

chlorine-35 chlorine-37

Classification of Elements

• MetalsMetals– Solids (except Hg), shiny, conduct electricity,

ductile, and malleable– Tend to give up electrons to form positive ions

• NonmetalsNonmetals – On right side of Periodic Table (except H)– Brittle, dull, poor conductors of electricity– Tend to accept electrons to form negative ions


• Metalloids (also called semi-metals)Metalloids (also called semi-metals)– B, Si, Ge, As, Sb, Te– Have some properties of metals and some of

nonmetals– Silicon is a semiconductor

• Does not conduct electricity at low voltages, but becomes a conductor at higher voltages


Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc Ti

Zr

V Cr Mn Fe Co Ni Cu Zn Ga

B C N O F Ne

He

Ar

Kr

Xe

Rn

Cl

Br

I

At

S

Se

Te

Po

P

As

Sb

Bi

Si

Ge

Sn

Pb

Al

In

Tl

Y

La

Ac

Hf

Rf

Nb

Ta

Db

Mo

W

Sg

Te

Re

Bh

Ru

Os

Hs

Rh

Ir

Mt

Pd

Pt

Ag

Au

Cd

Hg

H

1A

2A 3A 4A 5A 6A 7A

8A

3B 4B 5B 6B 7B 8B8B 8B 1B 2B

- -

Metals Metalloids Nonmetals

- - -

Classification of Elements, part 2

• Much info known about elements by mid 1800s

• Tried to organize elements in logical way

• Dmitri Mendeleev’s pattern worked best– Noted that certain properties tended to recur

periodically– Took elements in order of increasing mass– Placed elements with similar properties in same

column

Modern Periodic Table

• Elements arranged in order of increasing atomic number (# of protons)

• Elements with repeating properties are in the same group group or family family (column or vertical row)

• Elements in same periodperiod (horizontal row) change properties as you go across the period

.

Periodic Properties

• Mendeleev looked at both chemical and physical properties

Trend within Same Group

• The alkali metals, Group 1A elements

Cs

Rb

K

1ANa

Li3

Element

LithiumSodiumPotassiumRubidiumCesium

18098633928

1342883760686669

6.94111

22.99019

39.09837

85.46855

132.91

Melting Point(°C)

Boiling Point(°C)

Melting and boiling points decrease as you go down table

Group 1A: Alkali Metals• React with halogens to form compounds

such as NaCl

• Form +1 ions

• Very reactive

Cs

Rb

K

1ANa

Li3

Element

LithiumSodiumPotassiumRubidiumCesium

18098633928

1342883760686669

6.94111

22.99019

39.09837

85.46855

132.91

Melting Point(°C)

Boiling Point(°C)

Examples of Periodicity

• Fluorine, chlorine, bromine, and iodine fall in the same column

Cl

Br

I

7A

F

17

35.453

35

79.904

53

126.90

9

18.998

Examples of Trends in Periodicity

• The halogens, Group 7A elements

Cl

Br

I

At(210)

7A

F

Element

Melting Point(°C)

Boiling Point(°C)

FluorineChlorineBromineIodineAstatine

-220-101

-7114302

-188-3559

184337

9

18.99817

35.45335

79.90453

126.9085Melting and boiling points

increase as you go down table

Group 7A: Halogens

• Halogens exist as diatomic molecules, such as Cl2, F2, etc

• Halogens react with group I metals compounds such as NaCl

• Form -1 ions

• Very reactiveCl

Br

I

At(210)

7A

F

Element

Melting Point(°C)

Boiling Point(°C)

FluorineChlorineBromineIodineAstatine

-220-101

-7114302

-188-3559

184337

9

18.99817

35.45335

79.90453

126.9085

Examples of Periodicity

• The noble gases, Group 8A elements

He

8A

Ne

Ar

Kr

Xe131.3

Rn(222)

BoilingPoint(°C)

MeltingPoint(°C)Element

HeliumNeonArgonKryptonXenon

-272-249-189-157-112

-269-246-186-152-107

Radon -71 -62

2

4.00310

20.1818

39.9536

83.8054

86Melting and boiling points increase as you go down table

Group 8A: Noble Gases

• Do not react with other elements

• Do not form ionsHe

8A

Ne

Ar

Kr

Xe131.3

Rn(222)

BoilingPoint(°C)

MeltingPoint(°C)Element

HeliumNeonArgonKryptonXenon

-272-249-189-157-112

-269-246-186-152-107

Radon -71 -62

2

4.00310

20.1818

39.9536

83.8054

86

Why do elements in group have similar properties?

• Outermost Electron configurationOutermost Electron configuration is the same for all elements in a group

• Electron configuration:Electron configuration: the arrangement of electrons outside the nucleus

Electron Configuration

• Electrons are distributed in shells about the nucleus

Shell

Electrons the shellcan hold

4321

321882

Relativeenergies

of electrons in each shell

lower

higher.

nucleus

1st shell

2nd shell

3rd shell

4th shell


• Each shell (principal energy level) has a different maximum number of electrons it can hold

Shell

321

one 3s, three 3p, and five 3d orbitalsone 2s and three 2p orbitalsone 1s orbital

Orbitals contained in each shell

4 one 4s, three 4p, five 4d, and seven 4f orbitals

Maximum numberof electrons shell

can hold

22 + 6 = 82 + 6 + 10 = 182 + 6 + 10 + 14 = 32


• Shells (principal energy levels) are subdivided into orbitals

Shell

321





can hold

22 + 6 = 82 + 6 + 10 = 182 + 6 + 10 + 14 = 32


• Different kinds of orbitals have definite (and different) shapes and orientations in space


• Each orbital has a different energy

• Lowest energy fills first

Electron Configuration: Building Atoms

• Rule 1:Rule 1: Lowest energy orbitals fill first– The first three energy level orbitals fill in the

order 1s, 2s, 2p, 3s, and 3p

• Rule 2:Rule 2: Each orbital can hold a maximum of two electrons (with opposite spins)

• Rule 3:Rule 3: Orbitals of equal energy each add one electron first, then add second electron to fill them completely.

Order of Filling Orbitals

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s

Don’t just fill up one shell and then the next shell completely

Lowest energy fill first

Types of orbitals per shell

Shell

321





can hold

22 + 6 = 82 + 6 + 10 = 182 + 6 + 10 + 14 = 32

Orbital # orbitals/shell # electrons/

orbital type

s 1 2

p 3 6

d 5 10

f 7 14


• Orbital box diagramsOrbital box diagrams– a box represents an orbital– an arrow represents an electron– a pair of arrows with heads in opposite

directions represents a pair of electrons with paired spins

• ExampleExample: carbon (atomic number 6)

1s2 2s2 2px1 2py

1Expanded:

1s 2s

Electron configuration

Condensed:1s2 2s2 2p22px 2py 2pz

Electron Configuration Notation(Compact shorthand)

3p4

• 3 is principal energy level (shell)

• p is type of orbital (subshell)

• Superscript 4 show that there are four electrons in 3p orbitals


• Noble gas notation– the symbol of the noble gas immediately

preceding the particular atom indicates the electron configuration of all filled shells

• Example:Example: carbon (atomic number 6)

Electron Configuration(condensed)Orbital box diagram

Noble GasNotation

1s2 2s2 2p2 [He]2s2 2p2

Write the electron configuration for Vanadium (# 23)

Shorthand way of remembering

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

.

8A

1s7A6A5A4A3A

2B1B8B8B

1A

8B7B

2A

6B5B4B3B

1

2

3

4

5

6

7

1

2

3

4

5

6

7

6

7

Main group elements;s block (2 elements)

Transition elements;d block (10 elements)

Main group elements;p block (6 elements)

1s

Helium is also an s blockelement

3d

4d

5d

3p

4p

6d

2s

3s

4s

5s

6s

7s

2p

5p

6p

7p

4f

5f

Inner transition elements; f block

(14 elements)


• Lewis dot structures for the Group 1A (alkali) metals

Cs

RbCs•

K

Rb•

1A

K•

Na

Na•

Cs

Li•

Rb

Li

K

Na

Li

Element

NobleGas

Notation

Lewisdot

Structure

[He]2s1

[Ne]3s1

[Ar]4s1

[Kr]5s1

[Xe]6s1

3

6.94111

22.99019

39.09837

85.46855

132.91

Lewis Dot Structures

• Atomic symbol represents nucleus and core electrons

• Valence electrons shown as dots around symbol

N OB

H

Li Be

Na Mg

He1A 2A 5A 6A 7A 8A3A 4A

Cl

F

S

Ne

ArSiAl P

C

Ionization Energy

• Ionization energy:Ionization energy: the energy required to remove the most loosely held electron from an atom in the gaseous state– example: when lithium loses one electron, it

becomes a lithium ion; it still has three protons in its nucleus, but now only two electrons outside the nucleus

Li + Li+ + e-

Lithium Lithiumion

ElectronIonizationenergy

energy

Ionization Energy

• Ionization energy is a periodic property

Ionization Energy

• Ionization energy is a periodic property

– Increases as you move from left to right – Increases as you move up the table

Ionization energy


• Valence shell:Valence shell: the outermost incomplete shell

• Valence electron:Valence electron: an electron in the valence shell

• Core electron: Core electron: Electron inside the Electron inside the outermost shelloutermost shell

Electrons in Energy Levels

• The energy of electrons in an atom is quantizedquantized– An electron can have only certain allowed

energies

• Ground state:Ground state: the electron configuration of lowest energy

• Excited state:Excited state: Electron has more than lowest possible energy

Documents

Atoms Bettelheim, Brown, Campbell and Farrell Chapter 2