MATTER AND CHEMISTRYCH 4

I. Composition of Matter

A. Atom– Basic unit of matter– Can’t be broken down and still maintain its

properties

B. Structure of an Atom• Protons, neutrons, electrons• Proton: positive charge, in nucleus• Neutron: no charge, in nucleus• Electron: negative charge, outside nucleus

• Protons + neutrons = 99.99% of mass of atom• Electron exist in energy levels outside

nucleus– 1st energy level holds– 2nd energy level holds– 3rd energy level holds

C. Mass Number and Atomic Number

Mass number

Atomic number

# protons # neutrons #electrons

10B5

19F9

35Cl17

D. Isotopes and Radioisotopes# PROTONS #NEUTRONS #ELECTRONS

12C613C614C6

• Isotope:– Atoms of the same element with different

number of neutrons– Mass number is different– Atomic number and number of neutrons in the

same– All isotopes of the same element have the same

properties

• Radioisotope– Isotope that is radioactive– Nucleus is unstable and breaks doenover time

releasing energy– Uses:

II. Chemical bonds

A. Bohr Models

Atoms with filled outer energy levels are stable and wont bondAtoms with unfilled outer energy levels are unstable and bond to form molecules

B. Types of Bonds

1. Ionic bond

• Transfer of electrons between atoms• Forms ions• Donor atom becomes positive cation• Acceptor atom becomes negative anion• Oppositely charged ions attract

http://bcs.whfreeman.com/thelifewire/content/chp02/02020.html http://www.youtube.com/watch?v=QqjcCvzWwww

2. Covalent bond

http://bcs.whfreeman.com/thelifewire/content/chp02/02020.html http://www.youtube.com/watch?v=QqjcCvzWwww

• Sharing of electrons between 2 atoms

• Single bond:– Sharing of 1 pair of electrons between 2 atoms

• Double bond:– Sharing of 2 pair of electrons between 2 atoms

C. Electronegativity

• the degree to which an atom attracts electrons

• Atoms whose electronegativities are very different form ionic bonds

• Atoms whose electronegativities are about equal form nonpolar covalent bonds

• Nonpolar covalent bonds result from equal sharing of electrons

III. Water

• Use electronegativity table to predict the bond formed between:– Na and Cl– H and C– H and O

A. Polar Covalent Bonds

• The covalent bonds in water are polar covalent bonds

• Polar covalent bond: covalent bond where electrons are unevenly shared– Oxygen has a greater pull on the shared electrons

than hydrogen– Oxygen becomes slightly negative and hydrogen

becomes slightly positive

B. Hydrogen Bonds

• Water forms hydrogen bonds• Hydrogen bond: weak attraction between a

hydrogen atom with a partial positive charge and another atom with a partial negative charge

http://programs.northlandcollege.edu/biology/biology1111/animations/hydrogenbonds.html http://glencoe.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::550::400::/sites/dl/free/0078695104/383915/CH06_Properties_of_Water_103006.swf::Visualizing%20Properties%20of%20Water

C. Properties of Water1. Water is a good solvent• It dissolves other polar molecules and ions by

forming hydration shells around them

http://www.youtube.com/watch?v=EBfGcTAJF4o

2. Water has a high heat capacity• Heat capacity: amount of heat required to

raise temperature • Due to hydrogen bonds, a lot of NRG is

needed to make water molecules move faster, raising temp

• Water can absorb a lot of heat with minimal changes in temp

3. Adhesion and cohesion let water move up plant

• Cohesion: water molecules hydrogen bond to each other

• Adhesion: water molecules hydrogen bond to other polar molecules

• Transpiration: water evaporates out of leaves, pulling water up from root by cohesion and adhesion

• https://www.youtube.com/watch?v=mc9gUm1mMzc

4. Ice floats

• When water freezes, the molecules move farther apart making ice less dense than liquid water

• This allows marine animals to live below the ice

IV. Acids, Bases, pH, and Buffers

A. Water• H2O ↔H+ + OH-

• In water there are 10-7 moles H+ ions per liter of solution

B. Acids– pH < 7– Release H+ ions in solution

C. Bases– pH > 7– remove H+ ions from solution

D. pH scale– measures how much H+ ions in a solution– ex:

pH 7 =pH 3 =pH 9 =

E. Buffers– A weak acid or base that resists changes in pH by

reacting with strong acids or bases– This prevents sharp changes in pH– Buffers in body fluids help maintain homeostasis

• http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/buffer12.swf

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