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)  Ca 2+  (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 

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 

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 

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) CO 2 + H 2 o  H 2 CO 2

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  nimations/hydrogenbonds.html nimations/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 H 2 O separates into H3O and OH-  H+ loses electron to OH-  Equal parts of each ion  H 2 O has a neutral pH of 7

pH scale