Warm-up: Identify… A: substance or mixture (homogenous/heterogeneous) B: if it’s a substance further identify as element or compound Silver Salt water Air Oil in water Water Helium gas

Ch. 2.3 Elements and Compounds

1. Elements Def: simplest form of matter with unique set of (intensive) properties Listed in the Periodic Table 1 or 2 letters: first capital (usually the first letter of the common name), second lower case (if two elements start with the same letter)

Practice Hydrogen: H Helium: He What are the symbols for Neon, Nickel, Nitrogen who gets the N?

2. Compounds Def: Chemical combination of two or more elements in whole number ratios Example: H2O Subscript numbers refer to the element in front Actually should be written: H2O1 Ratio: 2 x H : 1 x O but 1 is never written in Chemistry!

Practice: Give the ratio of elements in… H2 Ratio: 2 x H H2O2 Ratio: 2 x H: 2 x O C6H12O6

Practice: Elements change characteristics when combined into compounds!!! Example: NaCl Na is a silvery metal, soft, explosive Cl is a green colored, aggressive gas NaCl is ____________________

Ch. 2.4 Chemical Reactions

Chemical Property Def: Ability to undergo certain chemical Rx Example: Iron binds oxygen to form rust Therefore: ability to rust is a chemical property of iron Fe + O → FeO (rust) Gold does not have this property! Gold does not rust!

Indicators of Chemical Rx If you mix two substances and you observe any one or more of the following…. Heating or cooling change in color Sound, explosions, light gas bubbles formation of a precipitate ….then a chemical Rx took place Note: Every chemical change always involves a transfer of energy which is often invisible

Law of the Conservation of Mass Matter cannot be created or destroyed in a chemical Rx But it often changes shape, consistency, state of matter but The mass of the product(s) must always equal the mass of the reactant(s) Note: if product weighs less, matter in form of gas has escaped!

Properties of Matter Properties of Matter

Warm-up List all characteristics you observed that are general markers that a chemical Rx had taken place during the Tic Tac Lab Write the Rx with reactants and products – use words since we do not know the exact formula for each