2.1 – The Nature of Matter

Atoms Basic unit of matter Particle Charge Location in Atom Proton Comes from word atomos, meaning “unable to be cut” further Consist of subatomic particles Particle Charge Location in Atom Proton Positive Nucleus Neutron Neutral Electron Negative Outside of Nucleus – occupying energy levels

Atoms Atoms are neutral because same number of positive particle (protons) as negative particles (electrons)

Elements and Isotopes Elements – Pure substance that consists of only one type of atom. Those things listed on the periodic table of elements Element Not an element Helium Water

C An Element in the Periodic Table 6 Carbon 12.011 Atomic Number – Number of protons (number of electrons) Carbon 12.011 Average atomic mass – Average of all isotopes Go to Section:

Simple Equations #P = #E AN = #P #P + #N = MN

Figure 2-2 Isotopes of Carbon has mass of 14 Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14 Decaying atom becomes 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 7 neutrons 6 electrons 6 protons 8 neutrons 90% of all carbon Has mass of 12 Radioactivity – lose neutrons Go to Section:

Elements and Isotopes Isotopes Atom that differs in number of neutrons they contain Identified by their various mass numbers Electron number determines chemical property and isotopes of the same element still have same number of electrons

Radioactivity – lose neutrons Figure 2-2 Isotopes of Carbon Section 2-1 10% of carbon has mass of 14 Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14 Decaying atom becomes 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 7 neutrons 6 electrons 6 protons 8 neutrons 90% of all carbon Has mass of 12 Radioactivity – lose neutrons Go to Section:

ELEMENTS and ISOTOPES How are radioactive isotopes useful? Used to date material based on the given rate at which isotope decays. Carbon dating

Half Life – Amount of time it takes for half of C14 to decay

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ELEMENTS and ISOTOPES Decaying isotopes – decay at a constant and predictable rate!!! 100 50 25 12.5 Same amount of time to lose half

Chemical Compounds Chemical Compound Substance formed by chemical combination (chemically bonded) of two or more elements Examples: Salt (NaCl), Water (H20), Glucose (C6H12O6) Two hydrogen atoms for every one oxygen Chemical Formula indicates that one sodium atom for every one chlorine atom

Chemical Bonds Covalent Bond Ionic Bond Form to make each atom “happy” = full outer electron shell (8 or 2) hold atoms in a compounds together two types Electrons are shared between atoms so that both have full outer shell Covalent Bond One or more electrons are transferred from one atom to another so that each can have full outer shell Ionic Bond

Chemical Bonds Sodium ion (Na+) Chloride ion (Cl-) Transfer Figure 2-3 Ionic Bonding Section 2-1 Chemical Bonds Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1

Transfer of electron Figure 2-3 Ionic Bonding Sodium atom (Na) Section 2-1 Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1 Go to Section:

Chemical Bonds Covalent Bonds electrons are shared between atoms so that each is stable (full outer shell) results in a Molecule

Chemical Bonds Carbon atom = 4 electrons in outer shell Carbon wants 8 Hydrogen atom = 1 atom in outer shell hydrogen wants two

Chemical Bonds Notice: by sharing electrons carbon has 8 electrons and hydrogen has 2 = Happy!