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Chapter 3 Atoms and Elements

3.1Classification of Matter

Matter

Matter is the “stuff” that makes up all things.

A pure substance is classified as

• matter with a specific composition.

• an element when composed of one type of atom.

• a compound when composed of two or more elements combined in a definite ratio.

Pure Substances

Elements

Elements are • pure substances that

contains atoms of only one type.

Copper, CuLead, PbAluminum, Al

Compounds

• contain two or more elements in a definite ratio.

Salt (NaCl)Table sugar (C12H22O11)Water (H2O)

Elements in a Compound

“Table salt” is a compound that contains the elements sodium and chlorine.

Mixtures

A mixture is a type of matter that consists of• two or more substances that are physically mixed, not

chemically combined.• two or more substances in different proportions.• substances that can be separated by physical

methods.

Physical Separation of a Mixture

Example: Pasta and water are separated with a strainer.

Homogeneous Mixtures

In a homogeneous mixture,

• the composition is uniform throughout.

• the different parts of the mixture are not visible.

Heterogeneous Mixtures

In a heterogeneous mixture, • the composition of

substances is not uniform.• the composition varies from

one part of the mixture to another.

• the different parts of the mixture are visible.

Classification of Matter

Identify each of the following as a pure substance or a mixture.

A. pasta and tomato sauce

B. aluminum foil

C. helium

D. air

Learning Check

Identify each of the following as a pure substance or a mixture.

A. pasta and tomato sauce mixture

B. aluminum foil pure substance

C. helium pure substance

D. air mixture

Solution

Identify each of the following as a homogeneous orheterogeneous mixture:

A. hot fudge sundae

B. air

C. sugar water

D. peach pie

Learning Check

Identify each of the following as a homogeneous orheterogeneous mixture:

A. hot fudge sundae heterogeneous mixture

B. air homogeneous mixture

C. sugar water homogeneous mixture

D. peach pie heterogeneous mixture

Solution

3.2Elements and Symbols

Elements are• pure substances that cannot be separated into

simpler substances by ordinary laboratory processes.

• the building blocks of matter.

gold carbon aluminum

Elements

Sources of Some Element Names

Some elements arenamed for planets,mythological figures,minerals, colors,scientists, andplaces.

A symbol• represents the name of an element.• consists of 1 or 2 letters. • starts with a capital letter.

1-Letter Symbols 2-Letter SymbolsC carbon Co cobaltN nitrogen Ca calciumF fluorine Al aluminum O oxygen Mg magnesium

Symbols of Elements

Several symbols are derived from Latin names as shownbelow.

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

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

Symbols from Latin Names

Physical Properties of Elements

The physical properties of an element • are observed or measured without changing its

identity.• include the following:

Shape DensityColor Melting pointOdor and taste Boiling point

Physical Properties of Elements

Some physical properties ofcopper are:

Color Red-orangeLuster Very shinyMelting point 1083 °CBoiling point 2567 °CConduction of electricity ExcellentConduction of heat Excellent

Select the correct symbol for each.A. Calcium

1) C 2) Ca 3) CA

B. Sulfur 1) S 2) Sl 3) Su

C. Iron1) Ir 2) FE 3) Fe

Learning Check

Select the correct symbol for each.A. Calcium

B. Sulfur 1) S

C. Iron3) Fe

Solution

Select the correct name for each symbol.A. N

1) neon 2) nitrogen 3) nickel

B. P1) potassium 2) phlogiston 3) phosphorus

C. Ag1) silver 2) agean 3) gold

Learning Check

Select the correct name for each:A. N

2) nitrogen

B. P3) phosphorus

C. Ag1) silver

Solution

3.3The Periodic Table

Groups and Periods

On the periodic table,• elements are arranged according to similar

properties.

• groups contain elements with similar properties in vertical columns.

• periods are horizontal rows of elements.

Groups and Periods

Periodic Table

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.

Names of Some Representative Elements

Alkali Metals

Group 1A (1), the alkali metals, includes lithium, sodium, and potassium.

Halogens

Group 7A (17), the halogens, includes chlorine, bromine, and iodine.

Identify the element described by the following:

A. Group 7A (17), Period 41) Br 2) Cl 3) Mn

B. Group 2A (2), Period 31) beryllium 2) boron 3) magnesium

C. Group 5A (15), Period 21) phosphorus 2) arsenic 3) nitrogen

Learning Check

A. Group 7A (17), Period 41) Br

B. Group 2A (2), Period 33) magnesium

C. Group 5A (15), Period 2

3) nitrogen

Solution

Metals, Nonmetals, and Metalloids

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 on the Periodic Table

Metals• are shiny and ductile.• are good conductors of heat and electricity.

Nonmetals• are dull, brittle, and poor conductors.• are good insulators.

Metalloids• are better conductors than nonmetals, but not

as good as metals.• are used as semiconductors and insulators.

Properties of Metals, Nonmetals, and Metalloids

Comparing a Metal, Metalloid, and Nonmetal

Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid.

A. sodium ____B. chlorine ____C. silicon ____D. iron ____E. carbon ____

Learning Check

Identify each of the following elements as 1) metal, 2) nonmetal, or 3) metalloid.

A. sodium 1 metalB. chlorine 2 nonmetalC. silicon 3 metalloidD. iron 1 metal E. carbon 2 nonmetal

Solution

Match the elements to the description.

A. Metals in Group 4A (14) 1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn

B. Nonmetals in Group 5A (15)1) As, Sb, Bi 2) N, P 3) N, P, As, Sb

C. Metalloids in Group 4A (14)1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb

Learning Check

Match the elements to the description.

A. Metals in Group 4A (14)1) Sn, Pb

B. Nonmetals in Group 5A (15)2) N, P

C. Metalloids in Group 4A (14)2) Si, Ge

Solution

3.4 The Atom

Dalton’s Atomic Theory

In 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.

Subatomic Particles

Atoms contain subatomic particles.

• Protons have a positive (+) charge.• Electrons have a negative (-) charge.• Neutrons are neutral.• Like charges repel and unlike charges

attract.

Rutherford’s Gold Foil Experiment

In Rutherford’s gold foil experiment, positively charged particles • were aimed at atoms of gold.• mostly went straight through the atoms. • were deflected only occasionally.

Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

Rutherford’s Gold Foil Experiment

Structure of the Atom

An atom consists• of a nucleus that

contains protons and neutrons.

• of electrons in a large, empty space around the nucleus.

Atomic Mass Scale

On the atomic mass scale,• 1 atomic mass unit (amu) has a mass equal to 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, 0.000 549 amu.

Particles in the Atom

Learning Check

Identify each statement as describing a1) proton, 2) neutron, or 3) electron.

A. found outside the nucleusB. has a positive chargeC. is neutralD. found in the nucleus

Solution

Identify each statement as describing a1) proton, 2) neutron, or 3) electron.

A. 3 found outside the nucleusB. 1 has a positive chargeC. 2 is neutralD. 1, 2 found in the nucleus

3.5Atomic Number and Mass Number

The atomic number• is specific for each element. • 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.

Atomic Number

Symbol

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.

Atomic Number and Protons

State the number of protons in each. A. A nitrogen atom

1) 5 protons 2) 7 protons 3) 14 protons

B. A sulfur atom1) 32 protons 2) 16 protons 3) 6 protons

C. A barium atom1) 137 protons 2) 81 protons 3) 56 protons

Learning Check

State the number of protons in each. A. A nitrogen atom

2) atomic number 7; 7 protons

B. A sulfur atom2) atomic number 16; 16 protons

C. A barium atom3) atomic number 56; 56 protons

Solution

An atom • of an element is electrically neutral; the net charge

of an atom is zero.• has an equal number of protons and electrons.

number of protons = number of electrons

Aluminum has 13 protons and 13 electrons. The net(overall) charge is zero.

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

Electrons in An Atom

Mass Number

The mass number• represents the number of particles in the nucleus.• is equal to the number of protons + the number

of neutrons.

Atomic Models

Number of protons = Atomic number

Number of protons + neutrons = Mass number

Number of neutrons = mass number – atomic number (protons)

Note: Mass number is given for specific isotopes only.

Study Tip: Protons and Neutrons

An atom of zinc has a mass number of 65.A. How many protons are in this zinc atom?

1) 30 2) 35 3) 65

B. How many neutrons are in the zinc atom?1) 30 2) 35 3) 65

C. What is the mass number of a zinc atom that has37 neutrons?1) 37 2) 65 3) 67

Learning Check

An atom of zinc has a mass number of 65.A. How many protons are in this zinc atom?

1) 30 (atomic number 30)

B. How many neutrons are in the zinc atom?2) 35 (65 – 30 = 35)

C. What is the mass number of a zinc atom that has 37 neutrons?

3) 67 (30 + 37 = 67)

Solution

An atom has 14 protons and 20 neutrons.

A. Its atomic number is1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

Learning Check

An atom has 14 protons and 20 neutrons.

A. It has atomic number1) 14

B. It has a mass number of3) 34 (14 + 20 = 34)

C. The element is1) Si (Atomic number 14)

Solution

3.6Isotopes and Atomic Mass

24Mg 25Mg 26Mg12 12 12

Isotopes• are atoms of the same element that have different

mass numbers.

• have the same number of protons, but different numbers of neutrons.

Isotopes

An atomic symbol• represents a particular atom of an element.

• gives the mass number in the upper left corner and the atomic number in the lower left corner.

Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol:

mass number 23 Na

atomic number 11

Atomic Symbol

The atomic symbol for a specific atom of an element

gives the

• number of protons (p+),

• number of neutrons (n),

• and number of electrons (e-).

Information from Atomic Symbols

Examples of number of subatomic particles for atoms

Atomic symbol

16 31 65O P Zn

8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n8 e- 15 e- 30 e-

Information from Atomic Symbols

Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following:

12C 13C 14C6 6 6

protons ______ ______ ______ neutrons ______ ______ ______

electrons ______ ______ ______

Learning Check

12C 13C 14C6 6 6

protons 6 p+ 6 p+ 6 p+

neutrons 6 n 7 n 8 nelectrons 6 e- 6 e- 6 e-

Solution

Write the atomic symbols for atoms with the following subatomic particles:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 47 e- ___________

Learning Check

A. 8 p+, 8 n, 8 e- 16O8

B. 17p+, 20 n, 17e- 37Cl17

C. 47p+, 60 n, 47 e- 107Ag47

Solution

Learning Check

1. Which of the pairs are isotopes of the same element?2. In which of the pairs do both atoms have 8 neutrons?

A. 15X 15X8 7

B. 12X 14X6 6

C. 15X 16X7 8

Solution

B. 12X 14X6 6

The atomic symbols in “B.” represent isotopes of carbon with 6 protons each, but one has 6 neutrons and the other has 8.

C. 15X 16X7 8

These isotopes of nitrogen and oxygen have 8 neutrons.

Isotopes of Magnesium

Isotopes of Sulfur

A sample of naturallyoccurring sulfur containsseveral isotopes with thefollowing abundancesIsotope % abundance

32S 95.02 33S 0.7534S 4.2136S 0.02

32S, 33S, 34S, 36S16 16 16 16

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

Isotopes of Some Elements and Their Atomic Mass

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

Atomic Mass for Cl

The atomic mass of chlorine is• due to all the Cl isotopes.• not a whole number.• the average of two isotopes:

35Cl and 37Cl.

Using the periodic table, specify the atomic mass ofeach element.A. calcium __________

B. aluminum __________

C. lead __________

D. barium __________

E. iron __________

Learning Check

Using the periodic table, specify the atomic mass ofeach element: A. calcium 40.08 amu

B. aluminum 26.98 amu

C. lead 207.2 amu

D. barium 137.3 amu

E. iron 55.85 amu

Solution

Calculating Atomic Mass

The calculation for atomic mass requires the

• percent(%) abundance of each isotope.

• atomic mass of each isotope of that element.

• sum of the weighted averages.

mass of isotope(1)x (%) + mass of isotope(2) x (%) + 100 100

35Cl has atomic mass 34.97 amu (75.76%) and 37C has atomic mass 36.97 amu (24.24%). • Use atomic mass and percent of each isotope to

calculate the contribution of each isotope to the weighted average. 34.97 x 75.76 = 26.49 amu

10036.97 x 24.24 = 8.961 amu

100 • Sum is atomic mass of Cl 35.45 amu

Calculating Atomic Mass for Cl

Calculating Atomic Mass Mg Isotope Mass Abundance

24Mg = 23.99 amu x 78.70/100 = 18.88 amu25Mg = 24.99 amu x 10.13/100 = 2.531 amu26Mg = 25.98 amu x 11.17/100 = 2.902 amu

Atomic mass (average mass) Mg = 24.31 amu

Atomic Mass of Magnesium

The atomic mass of Mg• is due to all the Mg

isotopes.• is a weighted average.• is not a whole number.

Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69Ga (atomic mass 68.926) atoms and 39.90% of 71Ga (atomic mass 70.925) atoms.

What is the atomic mass of gallium?

Learning Check

69Ga 68.926 amu x 60.10 = 41.42 amu (from 69Ga)

10071Ga70.925 amu x 39.90 = 28.30 amu (from 71Ga)

100Atomic mass Ga = 69.72 amu

Solution

3.7 Electron Energy Levels

Energy Levels

Energy levels• are assigned numbers n =

1, 2, 3, 4, and so on.• increase in energy as the

value of n increases.• are like the rungs of a

ladder with the lower energy levels nearer the nucleus.

Energy Levels

Energy levels have a maximum number of electrons equal to 2n2.

Energy level Maximum number of electronsn = 1 2(1)2 = 2(1) = 2 n = 2 2(2)2 = 2(4) = 8 n = 3 2(3)2 = 2(9) = 18

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.

Orbitals

A p orbital

• has a two-lobed shape.

• is one of three p orbitals in each energy level from n = 2.

An s orbital

•has a spherical shape around the nucleus.

•is found in each energy level.

Orbitals

Electron Level Arrangement

In the electron level arrangement for the first 18 elements • electrons are placed in energy levels (1, 2, 3, etc.),

beginning with the lowest energy level• there is a maximum number in each energy level.

Energy level Number of electrons1 2 (up to He)2 8 (up to Ne)3 8 (up to Ar)4 2 (up to Ca)

Learning Check

Write the electron level arrangement for each:

Solution

Write the electron level arrangement for each:

1. N 2, 5

2. Cl 2, 8, 7

3. K 2, 8, 8, 1

Learning Check

Identify the element with each electron level arrangement:

1. 2, 2

2. 2, 8, 3

3. 2, 7

Solution

Identify the element with each electron level arrangement:

1. Be 2, 2

2. Al 2, 8, 3

3. F 2, 7

3.8 Periodic Trends

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 in Group 5A(15) 2, 8, 5

All the elements in a group have the same number ofvalence electrons.

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

Be 2, 2Mg 2, 8, 2Ca 2, 8, 8, 2Sr 2, 8, 18, 8, 2

Groups and Valence Electrons

Periodic Table and Valence Electrons

Representative Elements Group Numbers1 2 3 4 5 6 7 8 H He1 2

Li Be B C N O F Ne2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8

Na Mg Al Si P S Cl Ar2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

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

1) 4 2) 6 3) 8

B. Al1) 13 2) 3 3) 1

C. Cl1) 2 2) 5 3) 7

Learning Check

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

B. Al2) 3

C. Cl3) 7

Solution

State the number of valence electrons for each. A. calcium

1) 1 2) 2 3) 3

B. group 6A (16) 1) 2 2) 4 3) 6

C. tin 1) 2 2) 4 3) 14

Learning Check

State the number of valence electrons for each. A. calcium

B. group 6A (16) 3) 6

C. tin 2) 4

Solution

For the element with the following electron arrangement:1) State the number of valence electrons.2) Identify the element.

A. 2, 8, 5B. 2, 8, 8, 2C. 2, 7

Learning Check

For the element with the following electron arrangement

1) State the number of valence electrons2) Identify the element.

A. 2, 8, 5 1) 5 2) phosphorus

B. 2, 8, 8, 2 1) 2 2) calcium

C. 2, 7 1) 7 2) fluorine

Solution

Electron-Dot Symbols

An electron-dot symbol• shows the valence electrons

around the symbol of the element.

• for Mg has 2 valence electrons as single dots on the sides of the symbol Mg.

. .·Mg · or Mg · or ·Mg or ·Mg

Writing Electron-Dot Symbols

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 ·

Groups and Electron-Dot Symbols

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

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

· Be ·· Mg ·· Ca ·· Sr ·· Ba ·

.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

.A. X is the electron-dot symbol for

1) Na 2) K

. .B. . X .

. is the electron-dot symbol of

2) N 3) P

Solution

Atomic Size

Atomic size is described

using the atomic radius;

the distance from the

nucleus to the valence

electrons.

Atomic Radius Within A Group

Atomic radius increasesgoing down each group of representative elements.

Atomic Radius Across a Period

Going across a period from left to right, • an increase in the number of protons increases

attraction for valence electrons.• atomic radius decreases.

Learning Check

Select the element in each pair with the larger atomicradius.

A. Li or KB. K or BrC. P or Cl

Solution

Select the element in each pair with the larger atomicradius.

A. KB. KC. P

Ionization Energy

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

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

Ionization Energy In a Group

Going up a group ofrepresentative elements,• the distance decreases

between nucleus and valence electrons.

• the ionization energy increases.

Ionization Energy

• Metals have lower ionization energies.

• Nonmetals have higher ionization energies.

Learning Check

Select the element in each pair with the higher ionizationenergy.

A. Li or KB. K or BrC. P or Cl

Solution

Select the element in each pair with the higher ionizationenergy.

A. Li B. BrC. Cl

chapter 3 atoms and elements - chemvision.netchemvision.net/10_chapter3_timberlake.pdf · in...

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