ESCS Review

Composition of Matter (Review) Matter – anything that takes up space and has mass. Mass – the quantity of matter an object has (the same as weight on Earth). Element – substances that cannot be broken down chemically into simpler kinds of matter. Atom – the simplest part of an element that retains all the properties of that element (tiny in size; would take 1 million to fill up the space of a period.) Nucleus – central region and the bulk of the mass of an atom.

Atoms and Elements 3 parts of an atom Protons – positively charged subatomic particle, part of the nucleus. Neutron – subatomic particle with no charge, other part of the nucleus. Electron – negatively charged subatomic particle, found outside the nucleus. Elements on the periodic table Atomic number – the number of protons an atom has. Mass number – number of protons + neutrons.

Atoms and Elements (continued) Atoms with different numbers of electrons or neutrons Ion – an atom or molecule with an electrical charge because of the gain (makes – ion) or loss (makes + ion) of an electron –Ex. Na+ and Cl- Isotopes – atoms of the same element, that have a different number of neutrons (would have the same atomic number but different mass number.) –Ex. Carbon-12, Carbon-13, and Carbon-14 How many neutrons would each of these have? Are there any beneficial uses for isotopes?

Electrons determine the properties of atoms Electrons determine the chemical properties of an atom –The farther from the nucleus, the greater its energy. –Occur at only certain energy levels (electron shells) –Those electrons in the outer shell are the ones that are involved in chemical bonds. They are called Valence Electrons. Valence electrons The outer shell of an element can contain up to 8 valence electrons. –All elements want to reach this number. This is when they have they are the most stable (have the least amount of energy). –The closer an element is to having 8 valence electrons, the more it wants to receive this electron. This is called Electronegativity. –As you travel to the TO THE RIGHT (because the 2 nd last column has 7 electron) and UP the periodic table, you become more electronegative

Molecules vs Compounds (Review) Molecule – 2 or more atoms joined together. Ex. O 2 Compounds – a molecule that is made up of atoms from two or more different elements. Ex. H 2 0 or NaCl

Chemical Bonds – the attractive forces that hold atoms together in molecules / compounds. 3 types of chemical bonds (1) Covalent Bond – forms when two atoms share one or more pairs of electrons. Can have single bond (share 2 electrons), double bond (share 4 electrons), or triple bond (share 6 electrons) 2 types Polar covalent bond - Unequal sharing of electrons when one of the atoms in the bond is more electronegative than the other. This creates a partially positive “pole” and a partially negative “pole”. Ex: H 2 O Nonpolar covalent bond – Equal sharing of electrons between two atoms that are identical. Ex. O 2

Chemical Bonds Continued (2) Ionic Bond – forms when electrons are transferred from one atom to another (when one atom is MUCH MORE electronegative than the other). The resulting positive and negative charges cause them to be attracted to each other (bonding). Ex. Na + + Cl - = NaCl

Chemical Bonds Continued –(3) Hydrogen Bond – very weak bond between partially positive hydrogen of 1 covalently bonded compound and a partially negative atom of another covalently bonded compound. 1 of these bonds is very weak, but many of them together are strong Responsible for holding water together

Energy (Review) Energy – the ability to do work. Chemical reaction – one or more substances change to produce one or more different substances. Energy is absorbed or released. Reactants – substances you start with in a reaction (left of the arrow). Products – substances you end up with after a reaction (right of the arrow). Activation energy – energy required to start a reaction.

Balancing Chemical Formulas _ H 2 + _O 2 _ H 2 0 _CH 4 + _O 2 _CO 2 + _H 2 0

Solutions (Review) Solution – mixture where one substance is uniformly distributed (dissolved) in another. Solute – the substance that is dissolved. Solvent – the substance in which the solute is dissolved. Concentration – the amount of solute in a solvent.