Matter Chapter 2

Matter can be classified as an element, compound or mixture… Elements- substances consisting of entirely the same atom. Compounds -substances made up entirely of the same molecule. Mixture- mix of elements and or compounds

Elements Substances made entirely of the same atom. There are 112 known atoms (so, 112 elements) 90 of those occur naturally Less than 40 of those can be found naturally in elemental form Hydrogen, copper, gold, magnesium, lead, oxygen, nitrogen, helium, etc. Elements can not be separated into other things.

Element Symbol Elements are represented by a 1-2 letter symbol The first must always be a capital letter, and the second (if present is lower case). C- carbon He- Helium

Element symbols you need to know He N Ne Pb Na Ni Ca S O Fe Au Cl H Cu C Ag helium- nitrogen- neon- lead- sodium- nickel- calcium- sulfur- oxygen- iron- gold- chlorine- hydrogen- copper- carbon- silver- *notice, that this is not written as FE, make that 2nd letter lower case not a small capital.

Compounds Pure substances made entirely of the same molecule Molecule- two or more atoms bonded together water, carbon dioxide, ammonia, glass, alcohol, and limestone

Separating Compounds Compounds can be broken down into simpler things *Although this requires a chemical change*

Representing Compounds This is done with element symbols and subscript numbers. H2O hydrogen (2) oxygen (1) Subscript numbers mean there are that many of the atom it is to the right of. If there is no subscript number then 1 is implied. Don’t write 1.

Here is where capitalization becomes really important 1 carbon, 2 oxygen carbon dioxide ( a gas) 2 cobalt atoms cobalt is a metal

Mixtures Compounds and/or elements mixed together but not bonded together. Substances that make up a mixture keep most of their own properties  Mixtures can be separated by simple physical means Iron and aluminum could be separated with a magnet Coffee grounds and water can be separated with a filter

Types of Mixtures Heterogeneous mixture- different throughout or chunky. Separation can be seen granite, orange juice with pulp, Italian dressing Homogeneous mixture- even throughout. The same throughout. No separation can be seen metal alloys, air around you, milk and saltwater

Chemical and Physical Properties and Changes

Physical Properties Any property that can be tested without changing the chemical make-up of the substance. For Example- mass, weight, density, volume, color, shape, texture, melting point, and boiling point. Changing phases does not change the chemical make-up of a substance. When water freezes to ice, it is still water (H2O).

Chemical Properties Any property that can only be tested by changing the chemical make-up of the substance. Flammability, chemical reactivity, and ability to rust.

Clues a chemical change has occurred…… it will often but not always cause bubbling, light, heat, color changes, an odor or a sound You can tell a chemical reaction has occurred if the products are different from the reactants! If there is no change it is NOT a reaction! e.g. ice melting is NOT a reaction, it is a physical change!

Chemical or Physical Changes are when you change a chemical or physical property cutting a piece of ice in half physical change activating an instant ice pack (make it cold) chemical change melting ice baking flour, sugar, egg and water together

Physical Properties can be used to separate mixtures Depending on the shape and size you may be able to separate them with a filter, or a centrifuge. Solutions require distillation (boiling substances off one at a time). Chemical properties could also be used to separate mixtures…

If it’s a compound… Physical properties can NOT be used to separate it. If its made of molecules, chemical properties can be used to separate it. Water can be separated into hydrogen and oxygen gas by electrolysis. (a chemical change)

Density

Density Density is a ratio of mass to volume of an object. D= m / v (density = mass / volume) Density is measured in g/mL (grams per milliliter). Density of a pure compound or element is a constant! Gold is always 19.3 g/mL, pure water is always 1.0 g/mL

Density Calculations Use the formula D = m / v If an object has a mass of 24 g and a volume of 48 mL, what is it’s density? D= 24 g / 48 mL = .5 g/mL If an object has a density of 1.5 g/mL, and it’s volume is 4 mL. What is it’s mass? 1.5 g = m / 4 mL = 6 g

Quick density test less dense objects float in more dense objects. least dense most dense cork oil plastic water penny

Floating Less dense things float, more dense things sink Helium is less dense than air so it floats A rock is more dense than water so it sinks

What is the density of… (compare them to water 1 g/mL) wood steel humans battleship less than 1 more than 1 about the same as 1 (unless it is sinking)

Interesting point… The density of steel is 7.9 g/mL The density of any ship is less than 1 g/mL, unless it has been sunk…… Boats have a hollow hull (big space for air to collect) to decrease their density. Air has a density of .0013 g/mL

Average Density Although a boat is made of steel you have to take the average density of the entire ship. The entire mass of everything divided by the entire space it occupies. The air significantly reduces its density. If the air is replaced with something (cargo or water) the density will increase and possibly cause it to sink.

Phase Changes

Phase Changes Change of state or a phase change is a conversion of a substance from one phase (solid, liquid, or gas) to another. All phase changes are physical changes as no new substance is made. That is, if you melt ice you started with H2O and ended with H2O.

Causing Phase changes Heating or cooling a substance can cause it to change phases. Heating is adding (heat) energy. Solid  Liquid  Gas Cooling is removing (heat) energy Gas  Liquid  Solid There is no such thing as cold energy or coldness you can add!

Names of Phase Changes Gas Solid Sublimation Deposition Vaporization Melting Liquid Freezing Condensation

Energy Changes in energy normally causes changes in temperature. It also takes energy to force a phase change. At the melting or boiling point heating or cooling won’t change the temperature.

So a graph would look like… Time vs. Temperature of water under constant heat boiling point 100oC 0oC now it is all steam temperature melting point it is now all a liquid time

Melting Point/Freezing Point and Boiling Point/Condensation Point There is no difference between the melting point (MP) and freezing point (FP) of a substance. Both are 0oC for water. The names only imply whether you are about to melt or freeze the substance! The same applies to the boiling point (BP) and condensation point (CP)