CHAPTER 2 COMPOSITION OF MATTER MATTER- anything that occupies space and has mass MASS- quantity of matter an object has ELEMENT- a pure substance that cannot be broken down into anything simpler kinds of matter (over 100 but fewer than 30 are important to living things)

ATOM The smallest unit of an element. The properties of an ATOM are determined by the number and arrangement of Protons, Neutrons, and Electrons

ATOM PROTONS- large particle with a POSITIVE charge found in the nucleus NEUTRONS- large particle with NO charge found in the nucleus ELECTRONS- small particle with a NEGATIVE charge- LOCATED IN ENERGY LEVELS

ATOMS ATOMS- have the same number of electrons and protons therefore they have no overall charge. ATOMS ARE ALWAYS NEUTRAL (although some are not stable in nature) ION- an atom that has lost or gained electrons and therefore has a charge - either negative ( gained ) or positive ( lost)

ATOMIC NUMBER of an element Is equal to the number of PROTONS found in the nucleus

ATOMIC MASS The total number of PROTONS and NEUTRONS in the nucleus.

WHERE ARE ELECTRONS? ELECTRONS EXACT LOCATION CAN NOT BE DETERMINED The best scientists can do is calculate the chance an electron in a given location due to the shading of the electron clouds. Since these clouds seem to be in rings at varying distances they are called ENERGY LEVELS or ORBITALS

ELECTRONS ORBITALS- regions in an atom where electrons are likely to be found. As the orbitals move further away from the nucleus the electrons must have more energy to occupy that space. Electrons will occupy the orbitals that require the lowest amount of energy first. 1 st energy level lowest energy level and can hold ONLY 2 ELECTRONS- 2 nd energy level- can hold 8 electrons 3 rd energy level- will be stable with 8 electrons.

How electrons fill up orbitals

VALENCE ELECTRON VALENCE ELECTRONS- electron that is found in the outermost energy shell, (has the most energy) and determines the atom’s chemical properties.

COMPOUND Defined as atoms of 2 or more elements that combine together chemically to form a new substance with different chemical properties Example hydrogen gas + oxygen gas = WATER Give me 3 examples of compounds.- Brainstorm

MOLECULE 2 or more atoms forming a chemical bond, smallest unit of a compound that retains the properties of that compound Example : H 2 O Two hydrogen atoms chemically bonded to one oxygen atom

Why are Compounds Made? Compounds are formed to make the atoms more stable. An atom is chemically stable WHEN ITS OUTERMOST ENERGY LEVEL IS FULL OF ELECTRONS

UNDERSTANDING THE PERIODIC TABLE What is a METAL? Where are they located on the periodic table? What is a NONMETAL? Where are they located on the periodic table? What is a NOBLE gas? Where are they located on the periodic table? Why are they called NOBLE?

3 types of bonds 1. METALLIC BOND- bond between two metals- 2. COVALENT BOND- bond between two non metals 3. IONIC BOND – bond between a METAL and NONMETAL

IONIC BOND IONIC BOND- the attraction of positive and negative electrical charges of the ions to each other. Step 1- Valence electrons are lost or gained and the atom becomes an ion Step 2- Ionic charges are attracted to each other Ionic bonds are easily broken in water and allow the water to conduct electricity

How can items with the same charge make a molecule? ANSWER- The SHARE the valence electrons Example O 2 and CO 2

COVALENT BONDS Two or more atoms share one or more pairs of electrons. Covalent bonds are much stronger than ionic bonds. IN your notes DRAW THE COVALENT BONDS of 2 hydrogen atoms and 1 oxygen atom to make a water molecule.

COVALENT BONDS In science we typically draw the covalent bonds by drawing a line between the two elements In science we typically draw the covalent bonds by drawing a line between the two elements One line- means the sharing of 2 electrons (1 pair) One line- means the sharing of 2 electrons (1 pair) Two lines- means the sharing of 4 electrons (2 pair) Two lines- means the sharing of 4 electrons (2 pair) Three lines- means the sharing of 6 electrons (3 pair) Three lines- means the sharing of 6 electrons (3 pair) Draw the symbol of a water molecule showing the covalent bonds Draw the symbol of a water molecule showing the covalent bonds

COVALENT BONDS ELEMENT NUMBER OF COVALENT BONDS EXAMPLES EXAMPLES Hydrogen Chlorine Fluorine Oxygen Sulfur Nitrogen Carbon