Matter & EnergyFoundations of the Natural World

Matter• If it exists, it’s matter▫You, a rock, oxygen…▫has mass; takes up space

(volume)•Fundamental unit: the atom•Atoms vary by # of protons ▫ each a different element

•Organized into the periodic table

•Can be changed, yet is always conserved

Energy•Makes things happen▫Do work▫Reorganize matter

•Comes in different forms▫in the chemical bonds of the

food we eat▫radiant energy from the sun

•Can be changed, yet is always conserved

Mass is energy? • In the early 20th century,

scientists hypothesized that mass and energy are linked.

•Albert Einstein provided the mathematical evidence with his famous equation, E = mc2

▫"E" ="energy," ▫"m" denotes "mass" ▫"c" is the speed of light

Atomic structure

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the ‘hood

Atomic structure

neutron

Proton: + chargeatomic nucleus

Electron: - charge

Sub-atomic structure

Up quark charge +2/3

Down quark charge -1/3

Some sub-atomic particles have sub-particles themselves!

e- ? Its a fundamental particle

Do the math!p = 2 ups, 1 downn = 1 up, 2 down

Unstable nuclei

• changes the number of protons • changes the element • a radioactive atom (more in C/D IS

year)

Potential problem in nucleus : like charges (++) repel

Neutrons break up charge; if they can’t, particles are ejected

Electrons orbit the nucleus

Orbit model vs Orbital model

• Negative electrons orbit the positive nucleus The first - nearest the nucleus - can hold up to 2 e-

The others hold 8e- or more , but are ‘full’ once they have 8

Element info

element

atomic number = protons infer electrons If p <> e, then an ion

symbol

atomic mass = nuclear mass # protons + neutrons why .003? Isotopes!

*a.m.u. = 1 atomic mass unit number of nuclear particles = mass number

Isotopes of H

1 a.m.u.* 2 a.m.u. 3 a.m.u.

Isotopes vary in # of neutrons

Electron dot model* – shows valence e-

*aka Lewis dot

6 e-

2•8•4 valence e-

The number of e- in the outermost orbitDetermines if the atom will form bonds

10 e-

2•8•8 valence e-

12 e-

2•18•2 valence e-

6 valence e • accepts 2 • -2 oxidation #

2 valence e- • donates 2 • +2 oxidation #

Determines which atoms are likely to bond with which other atoms is the outer orbit more empty, or more full?

It’s a match!

Oxidation Number determined by valence e-

Periodic patterns

Groups - Same valence/oxidation #

Periods - Same # shells/orbits

No stable isotopessynthetic

the element song

Periodic patterns

Periods - Same # shells/orbits

No stable isotopessynthetic

the element song

Ionic bonds

Valence stability achieved by moving an electron to another atom Creates charge imbalanceAtoms become ions

Positive & negative ions attracted to one another

Oppositely charged ions form an ionic bond

11 p+ 17 p+ 11 e- 17 e-

11p+ 17P+

10 e-18 e-

+

-

Oxidation: +1 -1

p+ to e- ratio: 11:10 17:18

Another view

Covalent bonds

Share electronsElectrons orbit both atoms equally

Atoms have an equal attraction to the electrons

Polar covalent bonds

Electrons more attracted to one atom type – reflects electronegativity

Share e- unequally

-+

+

Result? Regions of molecule are weakly positive and negative

Ionic Bonds

metal with non- metal very different valences electrons donated/accepted ex: NaCl

NaCl

go either way

17

Covalent BondsNon-metal with non-metalsimilar valenceselectrons shared ex: CO2

C O

go either way

4 6