Chapter 2

Study Guide

Dr. Joseph Silver

this chapter deals with- structure of atoms

- how atoms form molecules- the periodic table

- the control of chemical reactions

anything that has mass (made up of atoms)

andoccupies space (no matter how small)

is calledmatter

the word atomwas used 2000 years ago in Greece and

we still are learning more about atoms today

we have not yet been able to actuallyclearly see an atom

butscientists have done many experiments

whichshow that one or more electrons (-)

circle about a nucleuscontaining protons(+) and neutrons(0 no

charge)

atomic number = number of protons in an atom

atomic mass = mass of protons+neutrons+electrons

electron mass is so small that it contributesvery little to the mass of an atom

Atomic mass is also referred to asdaltons

the mass of a proton = 1 daltonthe mass of a neutron = 1 dalton

the mass of an electron = 1/2000th of a Daltonso atomic mass is mainly

the mass of protons and neutrons

remember mass represents the amount of matter in any atom, molecule or anything

else

weight represents the amount of force gravity

exerts on a substance

if you go to Mars your weight changesbut your mass does not change

the nucleus of an atom has protons and neutrons packed into the center of the atom

andthe electrons are located in circular orbits

(orbitals) or layers about the nucleus

-electrons travel so quickly that we cannot see one -they do not fly off due to their attraction to the

nucleus -atoms with large atomic numbers have many

orbital layers

when protons are equal to electrons - neutral atom

when protons do not equal electrons – atom is an ion

if there are more protons than electrons – positive cation

if there are more electrons than protons – negative anion

C12 = 6P + 6E + 6 neutrons C13 = 6P +6E + 7 neutronsC14 = 6P + 6E + 8 neutrons

atoms of an element with different number of neutrons are called isotopes

some isotopes release radioactive energy as the extra neutrons are released

isotopes have many uses in industry, medicine, chemistry, and biology

one use is to date the age of fossils

isotopes have a half lifewe know how long it takes for one-half of the

energy in an isotope to disappear and we use this information to compare the amount of an isotope in new material and in a fossil

and arrive at the age of the fossil

electrons determine the chemical behavior of atoms

how

when the outer electron shell of an atom is not full

it will give away electrons, or get electrons from other atoms, or share electrons with other atoms in order to have the outer shell filled

the farther an electron is from the nucleus the greater is the energy of the electron

likewisethe closer to the nucleus

the less energy in an electron

look at the drawings on pages 34the first electron layer can have 2 electrons

the second layer can have 8 electronsthese 8 are made up 4 orbitals each with 2

electrons(see fig 2.8)

for the purpose of this class any layer or orbital past the second orbital is

filled by 8 electrons

the electrons in the outer shell of an atom are referred to as valence electrons

and theseare the electrons available for chemical

reactions

-electrons are first added to the first shell (level)

-when it is full electrons are added to the next shell

-when the 2nd shell is full electrons are added to the 3rd

and so on for the 90 naturally occurring elements

as well as the laboratory manufactured elements

an atom with 1 electron in its first outer shell

would love to give it away or gain one so that

the outer shell a would be complete

an atom with 7 electrons in the outer shellwould love to find an atom to give it 1

electronand

an atom with 6 electrons in the outer shellwould love to find an atom to give it 2

electronsor 2 atoms to each give it 1 electron

in atoms with multiple shellsgaining electrons can fill the last

orbital levelor giving away electrons can empty the

last shell and

the lower level shell when it is filledbecomes the outer layer

see fig 2.12 page 38

on page B-1there is a full periodic table

showing the 90 natural elements as well as 28 man made elements

and onpage 34 there is a drawing showing the first

18 elements

in the periodic tablethe elements are arranged

according to their atomic number(the number of protons or electrons)

they are arranged in columns according to the number of electrons

in the outermost orbital shell

the electrons in the outer shellare called

valance electronsand they are located in the valence shell

these are the electrons whichare involved in chemical reactions

energy provides the ability to do workwhen an electron is released from its valence shell

the next lower orbit becomes the outer orbital shell

and the released electronreleases electron or atomic energy which is

used to power chemical reactions

look at the periodic table in the textbook-put a 1 over the H

-put a 2 over Be-put a 3 over B-put a 4 over C-put a 5 over N-put a 6 over O-put a 7 over F

-put an 8 over Hethe number represents the number of electrons present

in the outer shell of the elements in the column (H,Li,Na,K,Rb,Cs,Fr all have 1 electron in the

outer shell)(Be,Mg,Ca,Sr,Ba, Ra all have 2 electrons in the

outer shell)

an element with 1 electron in the outer shell can readily interact with an element having

7 valence electrons

an element with 1 valence electron can also readily interact with elements having 6

valence electrons

by exchanging or sharing electrons they fill

the outer shells and form compounds with stable atoms

ionic bonds form when atoms exchange electrons

and become positive and negative ionswhich are attracted to each other and form

a new molecule or compoundlook at fig 2.9

sodium gives up its 1 outer electron chlorine adds 1 electron to its 7 and fills the

shellsodium becomes positive by giving away an

electronchlorine adds an electron and becomes negative

the + and – ions attract to become sodium chloride

carbon has 4 electrons in its outer shelltwo carbons share their outer 4 electronsmaking an outer shell in each atom with 8

electronsthus each has a full outer shell with 8 electrons

forming a covalent bond

the electrons travel so fast that it is as ifthe 8 electrons are in both atoms at the

same time

when the atoms forming covalent bondsare similar in size the bonds may

be neutralbut

if one atom is much larger than the other then the covalent bond may show a degree of polarity

(one end of the molecule may be more positive or negative than the other end of

the molecule)

the ability of atoms to form chemical bonds is influenced by

- temperature (2x for every 10C)- concentration

-catalysts (enzymes)- pressure (keeps atoms closer together)

I will on many occasions mention the shape of a molecule

why

because molecules cannot talk to each othermolecules cannot use a phone to tell you

something

so

molecules react according to their shapethey fit together like pieces of a puzzle