Chem EOG review
3 classifications of matter Elements, compounds, mixtures
Element: made of one kind of atom Ex: Cu, O₂, Fe Compound: Made of two or more elements chemically joined together Has a fixed composition (ratio) of elements Has different properties than the elements that make it. Can only be broken down into elements by a chemical reaction. Ex: H₂O Mixture: Two or more different elements and/or compounds that are physically combined, NO CHEMICAL BONDING Can be homogeneous or heterogeneous Homogeneous (same throughout, solid/liquid/gas…ex: alloy, air) Heterogeneous (different throughout…pizza, muddy water) Can be easily separated into parts by physical methods (evaporation, chromatography, magnetism, filter) Often retains the properties of its components
Elements pure substance that cannot be separated into simpler substance by physical or chemical means.
NaCl H2O CO2 ≠ CO Compounds Pure substance composed of two or more different elements joined by chemical bonds. Two compounds made of different quantities of the same elements will have different properties Made of elements in a specific ratio that is always the same Has a chemical formula Can only be separated by chemical means, not physically CO2 ≠ CO
Mixtures A combination of two or more pure substances that are not chemically combined. substances held together by physical forces, not chemical No chemical change takes place Each item retains its properties in the mixture They can be separated physically Chem4kids.com
Can you identify the following? You will be shown a series of photos. Tell if each photo represents an item composed of an element, compound, or mixture. Review: An element contains just one type of atom. A compound contains two or more different atoms joined together. A mixture contains two or more different substances that are only physically joined together, not chemically. A mixture can contain both elements and compounds. Homogeneous Heterogeneous
Element, Compound, or Mixture? Copper
Element, Compound, or Mixture? Copper Cu
Element, Compound, or Mixture? Jelly Beans
Element, Compound, or Mixture? Jelly Beans
Element, Compound, or Mixture? Table Sugar
Element, Compound, or Mixture? Table Sugar C12H22O11
Element, Compound, or Mixture? Tea
Element, Compound, or Mixture? Tea
Element, Compound, or Mixture? Salt
Element, Compound, or Mixture? NaCl Salt
Element, Compound, or Mixture? Neon Gas
Element, Compound, or Mixture? Ne Neon Gas
Element, Compound, or Mixture? Salad
Element, Compound, or Mixture? Salad
Element, Compound, or Mixture? Pure Water
Element, Compound, or Mixture? Pure Water H2O
Element, Compound, or Mixture? Aluminum
Element, Compound, or Mixture? Aluminum Al
Element, Compound, or Mixture? Silver
Element, Compound, or Mixture? Silver Ag
Element, Compound, or Mixture? Sand
Element, Compound, or Mixture? Sand
Practice questions
Atom: basic unit of matter Element: A chemical element, or element for short, is a type of atom that is defined by its atomic number
Parts of atoms Proton + : large, positively charged subatomic particle, found in the nucleus Neutron 0 : large, neutral (no charge) subatomic particle, found in the nucleus Electron - : very small, negatively charged subatomic particle, located outside the nucleus in the large area called the electron cloud
Groups A group, also known as a family, is a vertical column in the periodic table of the elements. Groups are considered the most important way of classifying the elements. Elements within the same group have the same number of valence electrons, which is why they have similar chemical properties.
Periods A period is a horizontal row in the periodic table of the elements. The period number is equivalent to the number of electron energy levels (rings) in the element.
Number of protons Number of electrons Number of protons + neutrons Doesn’t include electrons because they weigh next to nothing TRY IT
Metals Conduct heat Conduct electricity Malleable Ductile Shiny Form + ions Iron, sodium, aluminum, gold
Metal families Alkali Group 1 extremely reactive Alkaline Earth Group 2 also very reactive Transition metals groups 3-12 not very reactive, used more commonly in industry ex: gold, silver, iron
Nonmetals Insulators (Do not conduct heat or electricity) Brittle Dull in appearance Form – ions Chlorine, bromine, neon, oxygen Many are gases at room temperature
Nonmetal families Halogens group 17 extremely reactive used in cleaning agents Ex: chlorine (Cl) Noble Gases group 18 do not combine to form molecules or compounds, exist as single atoms because they are stable. Noble gases have a complete (full) outer ring of electrons
Metalloids Found along the zig zag line Have properties similar to both metals and non metals Used in semiconductors Silicon (Si)
Atoms act toward stability and neutrality Stability = complete outer ring of electrons (2,8,8) Atoms combine with other atoms to complete their outer ring of electrons Neutrality= atoms seek an overall neutral charge which they can achieve by having the same number of protons (+) and electrons (-)
Atom Identity!! TRY IT Proton number (Atomic Number) identifies the atom. Atoms of the same element don’t always have the same number of neutrons…..same proton number but different neutron number = isotopes.
Compounds or molecules are represented using a chemical formula Subscripts (little number) tell you the number of atoms in the 1 molecule of the compound Coefficients (big number out front) tell you how many molecules (no number means the number is 1!)
practice
Conservation of Mass Mass on the reactant side of the equation equals the mass on the product side of the equation Number and type of atoms on the reactant side of the equation equals the number and type of atoms on the product side of the equation. Reactants Products
To check for balance, multiply coefficient x subscript Are these balanced? 3K + 2B2O3 2K2O + 2B 2Fe + 3Cl2 2FeCl3 KMnO4 +2HCl KCl + MnCl2 + H2O + Cl2 2C6HCOOH + 13O2 13CO2 + 2H2O To balance an equation its cool to change coefficients, do not change subscripts….don’t mess w/the little people (you’ll change the molecule’s identity!)
A reaction has 4 lead atoms in the products, according to the law of conservation of mass, how many lead atoms will be in the reactants? In a reaction, the mass of the reactants is 24g and 8g. Three products are formed, if the mass of two products is 3g and 7g, what is the mass of the third product?
practice
State of matter (solid, liquid, gas) Melting, freezing, boiling point Elements and compounds can be described by their chemical and physical properties Physical property: characteristic of a substance you can observe (using your senses) without changing it into something else State of matter (solid, liquid, gas) Melting, freezing, boiling point Magnetism Density Color Shape Malleability Solubility Specific heat
Chemical properties: properties of an element or compound in a chemical reaction pH Reactivity Flammability
Practice on Identifying Chemical and Physical Properties Water boils at 100 degrees Celsius. Diamonds are capable of cutting glass. Water can be separated by electrolysis into hydrogen and oxygen. Sugar is capable of dissolving in water. Vinegar will react with baking soda. Yeast acts on sugar to form carbon dioxide and ethanol. Wood is flammable. Aluminum has a low density. Ammonia is a gas at room temperature. Bromine has a red color.
Changes can be physical or chemical Physical changes do not rearrange atoms, I have the same substance I started with. I can reverse a physical change Change in shape Change in phase Dissolving These are easily Reversable
Chemical change: atoms are rearranged, I have different substances at the end of a chemical reaction/change Change in color Formation of precipitate (L+LS) Formation of a gas Creation of light Burning Change in temperature (exothermic, endothermic)
Practice on Identifying Chemical and Physical Changes You drop the spoon in the disposal and it bends Koolaid is dissolved in water Wood in a woodpile begins to decompose A campfire The process of respiration takes sugar and oxygen and creates water and carbon dioxide Making coffee Lightning converts N2 in the atmosphere to NO3
Energy in a chemical reaction Exothermic: releases more energy than it took to start Gets warm or releases light Endothermic: absorbs more energy than it releases Gets cold
RRR Questions