Matter Chemistry is the study of matter Matter takes up space and has mass Matter comes in many different forms
Chemical Elements Cannot be broken down 92 elements occurring in nature Symbol (different languages) 2 or 3 letters 25 elements are essential to life C, O, H, N Ca, P, K, S Fe, I These are the most common.
Compounds Two or more elements combined in a fixed ratio More common than pure elements WHY? Example: Na reacts? Cl reacts? NaCl reacts? Sulfuric Acid molecule
Isotopes - different atomic forms of the same element just different # of neutrons Radioactive isotopes – unstable because the nucleus decays spontaneously by giving off particles and energy
Helpful: biological tracers (plant studies, medicine, PET: positron- emission tomography) Harmful: damages cellular molecules (DNA) Half-life – time it takes for 50% of the radioactive atoms to decay
Energy Levels Why does an atom behave like it does? How much energy will an atom possess? Electron shells – different states of potential energy due to position in relation to nucleus (closer to nucleus, lower energy)
Orbital – 3-D shape where an electron is found How many in the 1 st electron shell? How many in the outermost shell? So the chemical properties of an atom depend on the number of electrons in the outermost shell.
Hydrogen Bonds -a hydrogen atom covalently bonds to one electronegative atom and is attracted to another electronegative atom Ex: water to water H2OH2O H2OH2O
Cohesiveness Cohesion – water molecules stick together because of hydrogen bonding Surface tension – difficult to stretch or break the surface of water (beads up) Adhesion – clinging of one type of substance to another type
Hydrophilic – water loving (clings to water) Capillary action – rising up a tube made of hydrophilic material (adhesion and cohesion together) Imbibition – water soaks into a porous material
Moderating Temperature Specific heat – amount of energy it takes to raise 1 Kg of a substance 1 o C --hydrogen bonds allow water to resist quick temperature changes
Heat – amount of energy associated with the movement of atoms and molecules Temperature – measures intensity of heat (average speed of atoms and molecules)
Heated water breaks hydrogen bonds --Molecules move faster and water absorbs a lot of heat (but temp. only warms a few degrees) Cooled water reforms hydrogen bonds --Molecules move slower and water releases a lot of heat (but only cools a few degrees)
Water requires a lot of heat to completely break all hydrogen bonds of a single water molecule so this decreases water’s tendency to evaporate --This is what gives water a high boiling point --When water does evaporate (heat energy is carried off), the remaining liquid water is cooled. Ex: sweating
Freezing of Water Why is water less dense as a solid? What is the significance of 4 degrees Celsius in water? --So water freezes when its molecules no longer move enough to break the hydrogen bonds
Acids, Bases, and pH When water molecules bond, the H-bond shifts around from one molecule to another allowing for a Hydrogen Ion and a Hydroxide Ion Dissociation – separation of a water molecule
An acid adds [H + ] to a solution A base reduces [H + ] in a solution so now it has more [OH - ] The product is the pH scale (potential hydrogen), which compresses the range of [H + ] and [OH - ] by using logarithms.
An acid adds [H + ] to a solution A base reduces [H + ] in a solution so now it has more [OH - ] The product is the pH scale (potential hydrogen), which compresses the range of [H + ] and [OH - ] by using logarithms.
7 is neutral, below 7 is acidic, above 7 is basic Buffers minimize changes in [H + ] and [OH - ] and are usually a weak acid or a weak base Ex: Carbonic Acid acts as a buffer in our blood.
Acid Rain Below pH 5.6 Caused by a reaction of water and sulfur oxides and nitrogen oxides in the atmosphere Harmful effects on terrestrial and fresh water ecosystems
Chemical Reactions The process of making and breaking bonds What are the 5 types? Synthesis Decomposition Single Replacement Double Replacement Combustion