The BIG Idea Everything around you is matter. All matter is made up of elements, the smallest unit of which is the atom, and is described by its properties and composition.
Objective 1 (CK) Atoms, Molecules, and Compounds Basics of atomic structure: nucleus, protons (positive charge), neutrons (neutral), electrons (negative charge) Atoms are constantly in motion; electrons move around the nucleus in paths called shells (or energy levels). Atoms may join together to form molecules and compounds. Common compounds and their formulas: Water: H20, “Table” salt: NaCl, Carbon dioxide: CO2
Objective 1 (CK) • People have been thinking about matter for more than 2, 500 years. It was widely believed that all matter was composed of four elements – earth, air, fire, and water
The Atom • In 1803, scientist and school teacher John Dalton came up with a precise definition for the invisible unit we call the atom today.
The Atom • We now know that atoms have an internal structure and area made of even smaller parts known as subatomic particles. These particles are protons, neutrons, and electrons.
The Atom • Protons are particles in the nucleus of an atom that have a positive (+) charge.
The Atom • Neutrons are uncharged (electrically neutral) particles that are also contained in the nucleus of an atom
The Atom • Electrons are negatively (-) charged particles that spin around the nucleus.
The Atom • Protons and electrons have exactly equal (but opposite) charges, so an atom tries to stay electrically “neutral” by having the same number of protons and electrons.
The Atom (Note that the number of electrons in any given atom is equal to its number of protons.)
The Atom Normally, an atom contains an equal number of electrons and protons, making the whole atom electrically neutral. This means that the negative charges of the electrons balance the positive charges of the protons in the atom.
The Atom If an atom loses any electrons , the atom become positively charged, and if it gains more electrons than protons, the atom becomes negatively charged. These positively and negatively charged atoms are called ions.
The Atom When an object discharges, it loses the excess electrons and becomes neutral again. Like charges repel and unlike charges attract.
The Molecule • Two or more atoms that are chemically combined are called Molecules. • Share one another’s electrons. • A water molecule consists of two hydrogen atoms that are bonded to an atom of oxygen.
Objective 2 (CK) Elements Elements have atoms of only one kind, having the same number of protons. There are a little more than 100 different elements. The periodic table organizes elements with common properties. Atomic symbol and atomic number Well known elements and their symbols
Objective 2 (CK) cont. Elements Two important categories of elements: metals and non-metals Metals compose about 2/3 of the known elements. Properties of metals: Most are shiny, ductile, malleable, conductive.
Elements • Matter is composed of elements. • Gold, silver, and aluminum, are all elements. • They are pure substances that cannot be broken down into simpler substances.
Periodic Table: Mendeleev • In 1869,Dmitri IvanovitchMendeléev created the first accepted version of the periodic table. • He grouped elements according to their atomic mass, and as he did, he found that the families had similar chemical properties. • Blank spaces were left open to add the new elements he predicted would occur.
Elements The Periodic Table arranges all elements according to their atomic number. atomic number = number of protons The table identifies elements with similar chemical properties.
Elements • Some elements you may know: • Oxygen – to breathe • Helium – makes balloons float • Calcium – helps make your bones strong • Iron – to stay healthy and strong
Properties of Metals • Metals are good conductors of heat and electricity. • Metals are shiny. • Metals are ductile (can be stretched into thin wires). • Metals are malleable (can be pounded into thin sheets). • A chemical property of metal is its reaction with water which results in corrosion.
Molecules • A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. • In the animation above, two nitrogen atoms • (N + N = N2) make one Nitrogen molecule .
Substances: element or compound • Elements- simplest kind of matter • cannot be broken down any simpler and still have properties of that element! • all one kind of atom. • Compounds are substances that can be broken down only by chemical methods • when broken down, the pieces have completely different properties than the original compound. • made of two or more atoms, chemically combined (not just a physical blend!)
Compounds • Atoms of two or more different elements bound together. • Can be separated into elements chemically, but not physically. In the animation above, water (H20) is a compound made of Hydrogen and Oxygen. Animated images and notes from http://www.chem.purdue.edu/gchelp/atoms/elements.html
Lets Review Atoms • The building blocks of Matter • Consists of Protons (+), Electrons (-), • and Neutrons (N). Elements • Consists of only one kind of atom, • Cannot be broken down into a simpler type of matter by either physical or chemical means • Can exist as either atoms or molecules. Images are from http://www.chem4kids.com
Chemical Bonds Molecules are groups of atoms held together in a stable association. Compounds are molecules containing more than one type of element. Atoms are held together in molecules or compounds by chemical bonds.
Objective 1 (CCSS) Describe that matter is neither created nor destroyed even though it may undergo change. Compare the total weight of an object to the weight of its individual parts after being disassembled. Compare the weight of a specified quantity of matter before and after it undergoes melting or freezing. Investigate the results of the combined weights of a liquid and a solid after the solid has been dissolved and then recovered from the liquid (e.g., salt dissolved in water then water evaporated). Investigate chemical reactions in which the total weight of the materials before and after reaction is the same (e.g., cream and vinegar before and after mixing, borax and glue mixed to make a new substance).
Compare the total weight of an object to the weight of its individual parts after being disassembled.
Objective 3 (CK, CCSS) Chemical and Physical Change Chemical change alters the composition of a molecule and results in a new substance with a new molecular structure. Examples of chemical change are the rusting of iron, the burning of wood, and milk turning sour.
Objective 3 (CK, CCSS) cont. Chemical and Physical Change Physical change alters only the properties or appearance of the substance, but does not change what the substance is made up of. Examples of physical change are cutting wood or paper, breaking glass, and freezing water.
Physical changes are those changes that do not result in the production of a new substance. If you melt a block of ice, you still have H2O at the end of the change.
If you break a bottle, you still have glass. Painting your nails will not stop them from being fingernails. Some common examples of physical changes are: melting, freezing, condensing, breaking, crushing, cutting, and bending.
Some, but not all physical changes can be reversed. You could refreeze the water into ice, but you cannot put your hair back together if you don’t like your haircut!
Special types of physical changes where any object changes state, such as when water freezes or evaporates.
Chemical changes, or chemical reactions are; changes that result in the production of another substance.
FLAMMABILITY: A material’s ability to BURN in the presence of OXYGEN
REACTIVITY:How readily (easily) a substance combines chemically with other substances.
When you burn a log in a fireplace, you are carrying out a chemical reaction that releases carbon. When you light your Bunsen burner in lab, you are carrying out a chemical reaction that produces water and carbon dioxide.
Common examples of chemical changes that you may be somewhat familiar with are; digestion, respiration, photosynthesis, burning, and decomposition.
Physical or Chemical Change? • Burning Paper • CHEMICAL
Physical or Chemical Change? • Digestion of food • CHEMICAL
Physical or Chemical Change? • Sugar dissolving in water • PHYSICAL
Physical or Chemical Change? • Iron turning red when heated • PHYSICAL