Chapter 3Atoms and Elements 1 3.1 Classification of Matter Copyright © 2009 by Pearson Education,...

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3.1Classification of Matter

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Matter

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

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Pure Substances

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.

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Elements

Elements are

• pure substances that contains atoms of only one type.

Copper, CuLead, PbAluminum, Al

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CompoundsCompounds

• contain two or more elements in a definite ratio.

Salt (NaCl)Table sugar

(C12H22O11)

Water (H2O)

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Elements in a Compound

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

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MixturesA 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.

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Physical Separation of a Mixture

Example: Pasta and water are separated with a

strainer.

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Homogeneous Mixtures

In a homogeneous mixture,

• the composition is uniform throughout.

• the different parts of the mixture are not visible.

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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.

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Classification of Matter

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Learning CheckIdentify each of the following as a pure substance or a mixture.

A. pasta and tomato sauce

B. aluminum foil

C. helium

D. air

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Learning CheckIdentify each of the following as a homogeneous orheterogeneous mixture:

A. hot fudge sundae

B. air

C. sugar water

D. peach pie

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Chapter 3 Atoms and Elements3.2

Elements and Symbols

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ElementsElements are

• pure substances that cannot be separated into simpler substances by ordinary laboratory processes.

• the building blocks of matter.

gold carbon aluminum

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Sources of Some Element Names

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

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Symbols of ElementsA symbol• represents the name of an element.

• consists of 1 or 2 letters.

• starts with a capital letter.

1-Letter Symbols 2-Letter Symbols

C carbon Co cobalt N nitrogen Ca

calcium F fluorine Al

aluminum O oxygen Mg

magnesium 17

Symbols from Latin NamesSeveral symbols are derived from Latin names as

shownbelow.

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

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

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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

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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

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Learning CheckSelect the correct symbol for each.A. Calcium

1) C 2) Ca 3) CA

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

C. Iron 1) Ir 2) FE 3) Fe

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Learning CheckSelect the correct name for each symbol.A. N

1) neon 2) nitrogen 3) nickel

B. P 1) potassium 2) phlogiston 3) phosphorus

C. Ag 1) silver 2) agean 3) gold

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Chapter 3 Atoms and Elements3.3

The Periodic Table

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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.

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Groups and Periods

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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.

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Names of Some Representative Elements

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Alkali Metals

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

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Halogens

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

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Learning CheckIdentify the element described by the following:

A. Group 7A (17), Period 4 1) Br 2) Cl 3) Mn

B. Group 2A (2), Period 3 1) beryllium 2) boron 3)

magnesium

C. Group 5A (15), Period 2 1) phosphorus 2) arsenic 3) nitrogen

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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.

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Metals, Nonmetals, and Metalloids on the Periodic Table

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Properties of Metals, Nonmetals, and MetalloidsMetals

•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.

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Comparing a Metal, Metalloid, and Nonmetal

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

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

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Learning CheckMatch 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

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Chapter 3 Atoms and Elements

3.4 The Atom

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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.

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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.

ElectronsThomson- Found that cathode ray consists of

tiny, negatively charged particles called electrons.

Electrons are emitted from electrodes made of two thin pieces of metal

Many different metals may be used to make electrodes Different metals contain different electrons

Cathode rays can be deflected by bringing either a magnet or an electrically charged plate near tube. This deflection depends on the strength of deflecting magnetic or electric field the size of the negative charge on the electron the mass of electron

Electron

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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.

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Rutherford’s Gold Foil Experiment

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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.

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Atomic Mass ScaleOn 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.

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Particles in the Atom

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Learning CheckIdentify 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

Learning CheckIs each of the following statements true or

false?Protons are heavier than electronsProtons are attracted to neutronsElectrons are small that they have no electrical

chargeThe nucleus contains all the protons and

neutrons of an atom

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3.5Atomic Number and Mass Number

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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

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Na

Atomic Number

Symbol

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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

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

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

B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons

C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons

Learning Check

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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

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Mass Number

The mass number

• represents the number of particles in the nucleus.

• is equal to the number of protons + the number of neutrons.

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Atomic Models

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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

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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 has

37 neutrons? 1) 37 2) 65 3) 67

Learning Check

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An atom has 14 protons and 20 neutrons.

A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is

1) 14 2) 16 3) 34

C. The element is

1) Si 2) Ca 3) Se

Learning Check