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Science 8: Unit on Matter Density – a comparison of mass (how much matter something has) and volume (how much space something takes up) - how “compact” something is the amount of matter for a certain volume of some substance Density = Mass/Volume (mass ÷ volume) Units are g/cm³ or g/mL - density is a constant property of matter each pure substance has its own specific density, it doesn’t matter how much of the substance you have density of pure water is 1.0g/mL an object sinks or floats in water depending on its density Density > 1.0 Sink Density < 1.0 Float - Density of liquids: liquids form layers depending on their densities The liquid with the lowest density will float on top Matter – anything that has mass and takes up space - made up of constantly moving particles with kinetic energy - the speed of the particle movement changes with temperature - as temperature↑ speed of the particles ↑ (adding heat energy) Phases of matter 1. Solid – matter that has definite shape and definite volume - examples: 2. Liquid – matter that has no definite shape, but has a definite volume - examples: 3. Gas – matter that has no definite shape and no definite volume - examples: - Particle Model of Matter – matter is made up of moving particles Solid - particles are tightly packed Liquid - particles are loosely packed Gas - particles are very far apart - low energy - medium energy - high energy - strong bond - bond stays connected but stretches - bond easily broken Phase change: adding heat energy will increase the motion of particles in a substance (heating) losing heat energy will decrease the motion of particles in a substance (cooling) every substance changes state at temperatures that are unique to that substance Melting – change of state from a solid to a liquid Freezing – change of state from a liquid to a solid Vaporization – change of state from a liquid to a gas Boiling – vaporization throughout the liquid Evaporation – vaporization from only the surface of a liquid Condensation – change of state from a gas to a liquid on the surface of an object (dew, clouds, steam, mist) Sublimation – surface particles of a solid change directly to a gas (dry ice) THE 'HEAT CURVE' FOR WATER Properties of Matter Physical – a property that can be observed without changing the substance into something else Examples: Phase of matter Ability to dissolve Color, odor, taste Density Hardness/texture Flexibility Conductivity Chemical – a property that can only be observed by changing a pure substance into something else Examples: Flammability Reactivity Physical Change – when matter experiences a change in size, shape or phase - changing the form or appearance of a substance but not the particles that make up the substance - examples: Chemical Change – a change in matter that produces a new substance - some evidence of chemical change is the production of heat or light, or the appearance of gas bubbles - examples: Temperature: a measure of how fast the particles of matter are moving (kinetic energy) Thermal Energy: the total energy of all the particles of matter Heat: the energy that is transferred between objects because of a difference in temperature - High temperature → Low temperature Thermal Expansion: as temperature increases the particles gain energy and move faster and farther away from each other -examples: Energy and Chemical reactions: Exothermic – energy is released and temperature increases o Heat given off o Examples: burning Endothermic – energy is absorbed and temperature decreases o Examples: photosynthesis Law of Conservation of Matter (Mass) and Energy: matter and energy cannot be created or destroyed, they can only change form Atomic Structure Atomic Theory – all matter is made up of atoms The atom is the smallest piece of matter that still has all the properties of that substance Particle Charge Location Mass (AMU) Electron Proton Neutron Negative Positive No charge Cloud Nucleus Nucleus 0 1 1_________ AMU = Atomic Mass Unit = 1.66 x 10 -24 grams The atomic nucleus has a positive charge with tightly packed protons and neutrons held together by a very strong bond Element Matter made of only one kind of atom Cannot be broken down into any other substance by physical or chemical means Represented by a chemical symbol o Gold – Au o Oxygen – O o Carbon – C o Sodium – Na Compound A substance made up of two or more elements that are chemically combined (bond) in a specific ratio Represented by a chemical formula with subscripts o Carbon Dioxide – CO2 1 carbon: 2 oxygen o Carbon Monoxide – CO 1 carbon: 1 oxygen Molecule A particle of matter made up of two or more atoms held together by a sharing of electrons Mixture Made up of two or more substances – elements, compounds, or both – that are physically combined Each substance keeps its characteristics Each substance can be separated out by magnetism, filtering, vaporization or distillation Atomic Number The number of protons in an atom of a certain element The number of electrons in an atom of a certain element # of protons = # of electrons # of positive charges = # of negative charges Atomic Mass The total mass of the atom The total number of protons plus neutrons in an atom of a certain element Each proton and each neutron have a mass of 1 AMU # of neutrons = atomic mass - atomic number Periodic Table Groups: vertical columns form families o # 1-18 o Similar arrangement of electrons Periods: horizontal rows o # 1-7 Shell Diagram – see atom packet for diagram Valence electrons The electrons that are farthest away from the nucleus They have the highest energy Can be from 1 – 8 in number The movement of valence electrons forms bonds between atoms by either sharing the electrons or transferring them Changing the number of neutrons and electrons 1. Cannot change the # of protons Atomic # = # of protons If you change the number of protons, you have a different atom 2. Adding or subtracting neutrons Changes the total mass of the atom Isotope – an atom of the same element with a different number of neutrons 3. Adding or subtracting electrons Gives atoms a charge – positive or negative Ion – a charged atom o Positive ion – has lost one or more electrons o Negative ion – has gained one or more electrons Metals – have common physical properties Hardness Shininess/luster Malleability – ability to be shaped Ductile – can be pulled into wire Conductivity – ability to transmit heat and electricity Magnetism …..and chemical properties Reactivity – tendency to give up (lose) electrons and chemically combine with other atoms Non-metals – generally have physical properties opposite of metals …….and chemical properties Reactivity – tend to take up (gain) electrons or are non-reactive (Group #18)