copyright©2004 by houghton mifflin company. all rights reserved. 1 elements, atoms & ions...

Copyright©2004 by Houghton Mifflin Company. All rights reserved.

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Elements, Atoms & Ions

Chapter 4


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Section 4.1 Elements• Over 112 known, of which 88 are found in nature

– others are man-made

• Abundance is the percentage found in nature– oxygen most abundant element (by mass) on earth and in

the human body– the abundance and form of an element varies in different

parts of the environment

• Each element has a unique symbol• The symbol of an element may be one letter or two

– if two letters, the second is lower case


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Sec 4.3 Dalton’s Atomic Theory

1. Elements are composed of atoms– tiny, hard, unbreakable, spheres

2. All atoms of a given element are identical– all carbon atoms have the same chemical and

physical properties

3. Atoms of a given element are different from those of any other element– carbon atoms have different chemical and physical

properties than sulfur atoms


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Dalton’s Atomic Theory

4. Atoms of one element combine with atoms of other elements to form compounds. – Law of Constant Composition

• all samples of a compound contain the same proportions (by mass) of the elements

– Chemical Formulas


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Dalton’s Atomic Theory

5. Atoms are indivisible in a chemical process.– all atoms present at beginning are present at

the end– atoms are not created or destroyed, just

rearranged– atoms of one element cannot change into

atoms of another element• cannot turn Lead into Gold by a chemical reaction


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Sec 4.4 Formulas Describe Compounds• a compound is a distinct substance that is composed

of atoms of two or more elements• number and type of each atom in the simplest unit of

the compound– molecules or ions

• each element represented by its letter symbol• the number of atoms of each element is written to the

right of the element as a subscript– if there is only one atom, the 1 subscript is not written

• polyatomic groups are placed in parentheses – if more than one


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Writing Formulas

Na2CO3

2 Na (Sodium) 1 C (Carbon) 3 O (Oxygen)


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4.5 Structure of the AtomAre atoms Divisible?

Dalton stated atoms are not divisible but experiments during the late 1890’s and early 1900’s proved otherwise


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• J.J. Thomson investigated (1890’s) using a device called a cathode ray tube


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• J.J. Thomson determined that the ray was made of tiny negatively charged particles we call electrons– he conclude that electrons were smaller than an atom– if electrons are smaller than atoms, they must be pieces

of atoms– if atoms have pieces, they must be breakable– Thomson also found that atoms of different elements all

produced these same electrons


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WilliamThomson’s (Lord Kelvin) Plum Pudding Model

Atom has structure

Electrons (distinct particles) suspended in a positively charged electric field

atom mostly “empty” space


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Rutherford’s Gold Foil Expt• How can you prove something is empty?• put something through it

– use large target atoms• use very thin sheets of target so do not absorb

“bullet”

– use very small particle as bullet with very high energy

• but not so small that electrons will affect it

• bullet = alpha particles, target atoms = gold foil


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Rutherford’s Gold Foil Experiment


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Rutherford’s Nuclear Model The atom contains a tiny dense center called the

nucleus The nucleus is essentially the entire mass of the

atom The nucleus is positively charged

the amount of positive charge of the nucleus balances the negative charge of the electrons

The electrons move around in the empty space of the atom surrounding the nucleus


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Structure of the Nucleus• The nucleus was found to be composed of two kinds

of particles• Some of these particles are called protons

– charge = +1– mass is about the same as a hydrogen atom

• Since protons and electrons have the same amount of charge, for the atom to be neutral there must be equal numbers of protons and electrons

• The other particle is called a neutron– has no charge– has a mass slightly more than a proton


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Sec 4.6 The Modern Atom

• We know atoms are composed of three main pieces - protons, neutrons and electrons

• The nucleus contains protons and neutrons

• The nucleus is only about 10-13 cm in diameter

• The electrons move outside the nucleus with an average distance of about 10-8 cm– therefore the radius of the atom is about 105 times

larger than the radius of the nucleus


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Sec 4.7 Isotopes• All atoms of an element have the same number of protons• The number of protons in an atom of a given element is the

same as the atomic number– found on the Periodic Table

• Atoms of an element with different numbers of neutrons are called isotopes

• All isotopes of an element are chemically identical– undergo the exact same chemical reactions

• Isotopes of an element have different masses• Isotopes are identified by their mass numbers

– mass number = protons + neutrons


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116C

126C

136C

146C

116C

Symbol of Element

Mass Number(protons + neutrons)

Atomic Number(protons)

Symbolic Notation


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•Average mass (reported on the periodic table) is calculated from the isotopes of an element weighted by their relative abundances.

Amu (mass of isotope) X abundance (decimal form)

The element copper has naturally occuring isotopes with mass numbers of 63 and 65. Cu-63 (mass 62.93 amu) is naturally found 69.2% and Cu-65 (mass 64.93 amu) is found 30.8%. Calculate the average atomic mass of copper.

Cu-63 62.93 amu X .692 = 43.54756

Cu-65 64.93 amu X .308 = 19.99844

63.546


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Elements• Arranged in a pattern called the Periodic Table• Position on the table allows us to predict properties

of the element• Metals

– about 75% of all the elements– lustrous, malleable, ductile, conduct heat and

electricity• Nonmetals

– dull, brittle, insulators• Metalloids

– also know as semi-metals– some properties of both metals & nonmetals


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4.8 The Modern Periodic Table

• Elements with similar chemical and physical properties are in the same column

• Columns are called Groups or Families

• Rows are called Periods

• Each period shows the pattern of properties repeated in the next period


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The Modern Periodic Table

• Main Group = Representative Elements– “A” columns

• Transition Elements– all metals

• Bottom rows = Inner Transition Elements = Rare Earth Elements– metals– really belong in Period 6 & 7


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4.9 Natural States of the Elements•States of elements are usually color- coded on tables. •Metals exist as solids at room temperature except Mercury. •Nonmetals can exist as solids, liquids or gases at room temperatures.

Diatomic elements- molecules made up of two atoms… there are 7 diatomic elements (molecules) that can never be found in nature uncombined.

7 diatomic elements… Hydrogen, Oxygen, Nitrogen, Fluorine, Chlorine, Bromine, IodineYou need to learn these!!! (HON & the Halogens)


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4.10 Ions• ions that have a positive charge are called cations

– form when an atom loses electrons

• ions that have a negative charge are called anions – form when an atom gains electrons

• ions with opposite charges attract – therefore cations and anions attract each other

• moving ions conduct electricity• compound must have no total charge, therefore we

must balance the numbers of cations and anions in a compound to get 0 total charge


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Atomic Structures of Ions• Metals form cations• For each positive charge the ion has 1 less electron than the

neutral atom– Na = 11 e-, Na+ = 10 e-

– Ca = 20 e-, Ca+2 = 18 e-

• Cations are named the same as the metalsodium Na Na+ + 1e- sodium ioncalcium Ca Ca+2 + 2e- calcium ion

• The charge on a cation can be determined from the Group number on the Periodic Table for Groups IA, IIA, IIIA– Group 1A +1, Group 2A +2, (Al, Ga, In) +3


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• Nonmetals form anions• For each negative charge the ion has 1 more

electron than the neutral atom– F = 9 e-, F- = 10 e-

– P = 15 e-, P3- = 18 e-

• Anions are named by changing the ending of the name to -ide

fluorine F + 1e- F- fluoride ionoxygen O + 2e- O2- oxide ion

• The charge on an anion can be determined from the Group number on the Periodic Table– Group 7A -1, Group 6A -2


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4.11 Electrical Nature of Matter

• Most common pure substances are very poor conductors of electricity– with the exception of metals and graphite– Water is a very poor electrical conductor

• Some substances dissolve in water to form a solution that conducts well - these are called electrolytes

• When dissolved in water, electrolyte compounds break up into component ions– ions are atoms or groups of atoms that have an electrical

charge


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4.11 Electrolytes & IonsSubstances that dissociate into ions when dissolved in water.


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Electrolytes

Strong(100% ions)

Weak Non(0% ions)

Aqueous Ionic Tap Water Covalent,

Solid Ionic

Strong Acids Weak Acids Pure Water

Strong Bases Weak Bases

copyright©2004 by houghton mifflin company. all rights reserved. 1 elements, atoms & ions...

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