Chemistry Wrap-Up

Matter Matter is anything that has mass and takes up space. Atoms are the smallest unit of matter Subatomic Particles: Proton: positive Neutron: neutral Electron: negative Nucleus: almost all mass, very dense, neutrons and protons, center of the atom

Matter An element is the smallest unit that can be considered a pure form matter, single atoms are all of a specific element which is determined by number of protons Two or more atoms can combine in specific ratios to form molecules

Elements and the Periodic Table There are a finite number of elements Elements on the periodic table are grouped according to similarities of their properties. Elements in the same family share similar characteristics

Combining Atoms The atoms of elements combine in ways that make up everything in the universe. It’s like Lego: you can build many different things with only 200 different blocks by combining different amounts of blocks in different ways.

Compounds, Elements, Mixtures, and Solutions Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. Solutions – a special kind of mixture where one substance dissolves in another.

Compounds, Elements, Mixtures, and Solutions cont. Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means. Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.

To classify matter: Is the matter uniform throughout? Can it be separated by physical means? Can it be separated by chemical means?

Molecular Motion Atoms and molecules move depending on their amount of energy (heat) When there is more energy, atoms are less attracted to each other and move faster When there is less energy atoms are more attracted to each other and move slower

Phases of Matter The movement of molecules causes matter to exist in three main phases: Solid: lowest energy Liquid: median Gas: highest energy

Properties of Matter All types of matter have specific properties that are unique to that type of matter and are independent of the size of the piece of matter

Density A measure of how tightly packed the molecules are in a piece of matter Density of 1g of gold is the SAME as the density of 100g of gold. Density is independent of sample size D=m/v

Other Examples All of these properties values are regardless of HOW MUCH of a sample you have Conductivity: how well a substance moves heat or electricity Solubility: how well something dissolves in water Magnetic properties: how magnetic something is

pH pH (potential hydrogen) A measurement of how acidic or basic a solution is Measured on a scale from 0-14 0-6: Acids 8-14: Bases 7: Neutral

Chemical Reactions Law of Conservation of Mass Mass is conserved, the number of atoms reacting is the same as the number of atoms that make the product.

Physical v. Chemical Change Chemical Changes The chemical make-up of the substance is different. Color change, fire, new smell, precipitate Physical Changes The substance is chemically the same Crumpling paper, ice melting

Temperature and Chemical Change A higher temperature will increase the speed of a reaction A lower temperature will decrease the speed This is because of the motion of the molecules