The Nature of Matter

Chapter 2

Atoms

Smallest particle of an element Structure of the atom

Nucleus: Protons (+) Neutrons (no charge)

Orbital cloud: Electrons (-)

Move rapidly can be gained or lost

Outer levels have a higher energy

Atoms

Duet rule: the closest orbital around the

nucleus can hold 2 electrons Octet rule:

the cloud orbitals can hold up to 8 electrons

This causes attraction between atoms

Atoms

Neon atom 10 protons 10 neutron 10 electrons

Duet Rule

Octet Rule

Stable element

Atoms

Charge of the atom Sum of protons and electrons

If number of protons = number of electrons no electrical charge

Atoms

Ion: charged particle lose or gain electron

Cl- (gained 1 electron)

Na+ (lost 1 electron)

Ca2+ (lost 2 electrons)

Elements

Element Substance that cannot be

chemically broken down further

Consists of entirely one atom

Elements

Mass of the atom Sum of protons and

neutrons Atomic #

Number of protons

Isotopes

Isotopes Amount of protons ≠

number of neutrons Can be more or less Atomic mass is average

masses of element’s isotopes

Isotopes

Radioactive isotopes Unstable nucleus and break down at a

known rate over time Give off radiation which may be dangerous Many uses in science

Tracers to follow movement within organisms

Ex: Carbon-14 can be used to detect the age of ancient bones

Chemical Compounds

Compound Substance that can be broken

down to elements (2 or more elements)

97% of all compounds contain only 6 elements

C-H-O-N-P-S C-H-O-N = 64%

Chemical Bonds

Atoms in compounds are held together by various types of bonding

Which part of the atom is involved in bond formation?

Bonds form by using valence electrons

What types of bonds are there? Ionic and covalent

Ionic Bond

Ionic bond Electrons are transferred Attraction between oppositely

charged ions Ex: Na transfers e- to Cl Na+Cl- Become charged particles by

gaining or losing electrons

Ionic Bond

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

Covalent Bonds

Covalent bond Pairs of electrons in outer shell

shared by both atoms Can be single (2 electrons) or

double (4 electrons)

Covalent Bond

http://www.youtube.com/watch?v=1wpDicW_MQQ

States of Matter

Solid Maintains fixed volume and shape Atoms are more likely linked to each other

Liquid Maintains a fixed volume Particles move more frequently Ability to flow and change into any shape

Gas Particles move rapidly Fill volume of container occupied

States of Matter

http://www.youtube.com/watch?v=s-KvoVzukHo

Chemical Reactions

One or more substances is made or broken down

Reactants On the left side of an equation Starting substance(s)

Products On the right side of an equation Ending substance(s)

CO2 + H2o H2CO2

Activation Energy

Energy needed in order for a reaction to occur

Substances known as catalysts can lower the activation energy to make a reaction start faster Living things have catalysts are called enzymes that

speed up reactions

Demonstration

Are the pieces of paper without water more attracted to each other?

Why are the pieces of paper with water easier to stick together?

What is holding the papers together? Water is a polar molecule Partial negative pole and partial positive

side

Polarity

An uneven distribution of charges within a molecule

In a water molecule the oxygen atom has a greater ability to attract electrons to it, which pulls the hydrogen atoms to one side

Hydrogen bonding

Due to partial positive and partial negative poles on the water molecule, other water molecules are attracted to each causing a hydrogen bond

Not as strong as covalent or ionic bonding

Hydrogen Bond

http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html

What are the other unique properties of water?

Cohesion: The ability for water to be attracted to itself (due to Hydrogen bonding)

Cohesion – Surface Tension

Adhesion - The ability for water to be attracted to other substances

Adhesion - Capillary Action

How water moves up plants

Plant tubes (xylem) are made of cellulose which is polar

Water molecules are attracted to the sides of thin tubes of xylem

What do you think will happen to the daisies?

Capillary Action

How water moves up plants

Water molecules are attracted to the sides of thin tubes plant walls

This is also why water moves up a straw without you doing anything!

Activity!

Drops of water on a penny

What properties of water are shown in this experiment?

pH

pH is the concentration of Hydrogen ions in a solution

It is the “potential of Hydrogen”

Strong Acid and Base

HCl – hydrochloric acid Strong acid Solution would have a HIGH concentration of H+

ions H+ loses electron to Cl-

NaOH – sodium hydroxide Strong base Solution would have a HIGH concentration of OH-

ions Na+ loses electron to OH-

Buffers

Weak acids/bases that react with strong acids or bases to have a gradual shift in the pH scale

Ex: Milk calming stomach acid

Why is water neutral?

The molecule of H2O separates into H3O and OH- H+ loses electron to OH- Equal parts of each ion H2O has a neutral pH of 7

pH scale