Chemistry Chemistry is the science of matter and the changes it - PDF document

Chemistry Chemistry is the science of matter and the changes it undergoes What is matter? (as it is related to biology) Matter Matter is anything that takes up space and has mass All living and nonliving matter is composed of http://en.wikipedia.org/wiki/Matter ~ 92 naturally-occurring basic elements (as seen on a Periodic Table) Mass = quantity of matter an object has - different from weight = force of gravity on an object (weight = mass * gravity) Elements Elements are pure substances that cannot be broken down to substances with different chemical or physical properties. Six elements ( C, H, N, O, P, S ) make up 98% of living things.

Atomic Models Atoms - we will use the model proposed by Danish physicist Niels Bohr in 1913 • Atom = the simplest particle of an element that - Bohr model of an atom = electrons 'orbit' nucleus has all the properties of that element like planets orbit the sun • Scientists use models to describe the structure of atoms Atomic Structure The Nucleus Chemical and physical properties of elements depend upon the subatomic particles of the atom. Protons - positively (+) charged particles Neutrons – particles with no charge Atoms of an element contains a specific number of protons , neutrons , and electrons . Both - have about 1 atomic mass unit (amu) of mass (aka 1 dalton) - in nucleus of atoms The Properties of an Element Relative Atomic mass ('weight') of an atom is The Electron 'Cloud' about equal to the sum of its protons and neutrons. Atomic number = the number of protons Electrons - negatively (-) charged particles - you can find the number of neutrons by - move around nucleus subtracting the atomic number from the atomic - negligible mass (~0 amu) mass! - each element has a chemical symbol

Some models of some elements: The Properties of an Element An atom of a pure element is electrically neutral because... Neutrons have no charge The number of protons always equals the number of electrons An electron is as negative as a proton is positive Isotopes Isotopes are atoms with the same number of protons Isotopes but a different number of neutrons - for ex. - a carbon atom has six protons but may - because neutrons are electrically neutral they have more or less than usual six neutrons. don't affect the element's chemical properties, unless there are just too many or too few neutrons then the isotope may become unstable (radioactive) - radioactive isotopes decay over time Half-Life Isotopes - one half-life = the amount of time it takes for half the mass of a substance to decay - for ex. - A carbon with eight rather than six neutrons is unstable; it releases rays and subatomic particles and is a radioactive isotope

Isotopes in Biology - Low levels of radiation such as radioactive iodine or glucose allow researchers to trace the location & - High levels of radiation can cause cancer/destroy activity of the atom in living tissues cells - these are called tracers (used in CAT scans) - careful use of radiation can sterilize products & kill cancer cells -measuring the amount of radioactive isotopes and comparing that to the non-rad. isotopes allows scientists to tell how old something is ex. radiocarbon dating for fossils Electrons Electrons and Energy - electron cloud = 'cloud' around nucleus where e - are more energy = farther away from nucleus - electron shell = 'shell' or ring around nucleus less energy = closer to nucleus where e - are found inner e - shells = lower energy level - energy level = describes an e - location based on outer e - shells = higher energy level how much energy it has Orbitals - orbital = a volume of space where an e - is most likely to be found atomic structure http://youtu.be/pV822HfqT44

Electron Shells Electron Shells - the 1st shell is complete with 2 e - - the 2nd shell is in the shell model: electron configuration = # of e - complete with 8 e - in each e - shell - 3rd is stable with 8 e - ex. S - 2,8,6 C - 2,4 Na - 2,8,1 but full w/18 valence number = # of e - in the outer e - shell - every atom 'wants' to -determines how an element will react have a complete outer shell Electron shells Noble Gases The Octet Rule - some elements have a full outermost e - shell – generally, atoms want to have 8 electrons these are called the noble gases – and they won't react with other elements in their outer e - shell they’re in group 18, far right of PT: http://www.sciencemusicvideos.com/the- Helium Neon Argon Krypton octet-rule-song/ Xenon Radon Electron Dot Structures show the valence e- as dots surrounding the elemental symbol ● Cl has 7 valence e- ● they are drawn in pairs so unpaired e- are visible

Compounds Chemical Reactions - When two or more different elements react or bond - most elements tend to undergo - together, they form a compound (ex. H 2 O) chemical reactions = atoms combining in - compound = pure substance made of 2 or more order to become more stable (fill their elements outermost e - shell) ex. water, methane (CH 4 ), glucose (C 6 H 12 O 6 ) Chemical Bonds - molecule = smallest part of a compound that has the properties of the compound (one - Bond = an attachment between atoms molecule of water vs. a lot of water molecules) - Electrons possess energy -> bonds that exist compound is the type of molecule like element between atoms in molecules contain energy is the type of atom -> it requires energy to break & form chemical bonds Ionic Bonding Ionic Bonding - Ionic bonds = form when e - are transferred - ions = charged particles that have lost or from one atom to another gained e - - By losing or gaining e - , atoms in ionic - positive ions = cations = lost e - reactions fill their outer e - shells, and are more - negative ions = anions = gained e - stable

Ionic Bonding - Example: sodium (Na) with one less e- has pos. charge; chlorine (Cl) has extra e- that has neg. charge - Attraction of oppositely charged ions holds the 2 atoms together in an ionic bond How do we tell what elements will form ions and/or ionic bonds? -# of valence electrons - if low, will tend to lose e- if high, will tend to gain e- Ionic bonding video http://youtu.be/xTx_DWboEVs Covalent Bonds Ionic Bonds - Covalent bonds = 2 atoms share 1 or more tend to form between metals and nonmetals e- so each atom has full outer e- shell - H can form either ionic or covalent bonds position on ion charge - can lose an e - to become H+ or share an e - periodic table complete its outer shell of two e - Metal left positive Nonmetal right negative

Structural Formulas Oxygen shares 2 electrons to form a - shared e- are shown as a line between two atoms double covalent bond - ex. single covalent bond (H-H), double covalent bond (O=O) - 3D shape of molecules is not represented by structural formulas, but can show bond angles Molecular Models Covalent bonding video http://youtu.be/1wpDicW_MQQ How do we tell what elements will form covalent bonds? -they tend to form between 2 (or more) nonmetals -# valence e - - elements still ‘want’ to complete outer e - shells

Nonpolar and Polar Covalent Bonds - nonpolar covalent - oxidation number = the hypothetical bonds = sharing of e - charge an atom would have if all bonds it is equal formed were 100% ionic - polar covalent bonds = sharing of e - for ions - charge = oxidation # is unequal for elements in covalent bonds = what the - ex. In water (H 2 O), sharing of e - by oxygen charge would be if it were ionic… and hydrogen is not for pure elements = zero equal Hydrogen Bonding Electronegativity - hydrogen bond = weak attractive force - Attraction of an atom for electrons in a between slightly positive hydrogen atom of one covalent bond is called electronegativity molecule and slightly negative atom in another - more protons = more electronegative or the same molecule - the oxygen atom is more electronegative - Many hydrogen bonds taken together are than the hydrogen atom - the pair of e - shared in water is more relatively strong - Hydrogen bonds between complex molecules attracted to the Oxygen atom of cells help maintain structure and function - oxygen takes on a partial negative charge - the hydrogen atoms in water take on a partial positive charge Energy Hydrogen Bonding - energy = the capacity to do work - electrons have energy → atoms have energy → all things are made of atoms → all things have energy - electrons are moving → atoms are moving → all things are made of atoms → all things are moving - the amount of movement of atoms determines the state of matter

Solids Liquids - the least amount of - more movement/ movement (vibration energy only) - takes shape of its - particles have the container least energy - fixed volume and shape Plasma Gases - even more movement/ - ionized gas energy - ions and electrons - fills volume of - also no definite shape container or volume - no definite shape - may generate magnetic fields and electric currents - ex. Stars, lightning Energy and Chemical Reactions The 4 States of Matter - chemical reactions involve the transferring or sharing of electrons and therefore involve energy - all reactions require energy to begin - activation energy = amount of energy needed to start a chemical reaction (E A ) https://www.youtube.com/watch? v=VbIaK6PLrRM