Basic Chemistry Lecture 1 Know the definitions of elements atoms compounds and molecules Element a substance that cannot be broken down into a simpler substance in a chemical reaction Elements can combine to form compounds Atom the smallest unit of an element retaining its properities Compounds combinations of elements in different proportions Elements An element s properties depend on the structure of its atoms Each element consists of unique atoms An atom is the smallest unit of matter that still retains the properties of an element Atoms are composed of subatomic particles Neutrons no electrical charge Protons positive charge Electrons negative charger Atomic Number vs Atomic Mass Neutrons and protons form the atomic nucleus Neutron mass and proton mass are almost identical Atomic masses are expressed in terms of Daltons Neutrons and protons have a mass of 1 dalton Atomic number and atomic mass Atoms of the various elements differ in number of protons and neutrons An elements atomic number is the number of protons in its nucleus for uncharged atoms this is also the number of electrons An elements atomic mass is the sum of protons and neutrons in the nucleus If given atomic number atomic mass and charge you can calculate complete composition in terms of number of protons neutrons and electrons what is the atomic number and atomic mass of atom that has 6 protons 6 neutrons and 6 electrons A 6 12 atomic number number of protons atomic mass protons neutrons Flourine s atomic number is 9 and its atomic mass is 19 How many neutrons and electrons does an uncharged atom of fluorine have A 10 9 You subtract the atomic mass 19 by the atomic number 9 to get the number of neutrons because remember the atomic mass is both neutrons and protons Isotopes All atoms of an element have the same number of protons but may differ in number of neutrons Isotopes are two atoms of an element that differ in number of neutrons Isotopes are the same element and have the same chemical properties but may have different physical properties Examples Carbon Isotopes 12C is the most common form of carbon 13C magnetic very rare 14C radioactive even rarer these carbons have the same atomic number 6 but differ in atomic masses due to different number of neutrons radioactive isotopes are unstable Their nuclei decay spontaneously giving off subatomic particles and energy so pretty much an isotope is an element that has different numbers of neutrons NOT protons The Energy Levels of Electrons Electrons have differing amounts of potential energy Energy is the capacity to do work or to cause change Potential energu is stored energy that matter has because of its location or structure An electrons state of potential energy is called its energy level and is determined by its location relative to the nucleus That location is called the electron shell it is in Electrons in lower shells have less energy Each shell has orbitals and each orbital can hold two electrons This first shell has one orbital and can hold only two electrons the next two shells have 4 orbitals and can hold a maximum of 8 electrons Think of the shells like the rings in the picture and orbitals are the pairs of electrons that bunch together Atoms Stability Atoms attempt to gain or loose electrons until the outer shell has 8 paired electrons Oxygen has 2 unpaired electrons in the outer shell which explains why oxygen can only form two bonds Carbon has 4 unpaired electrons in outer shell and explains why carbon can only form four bonds Making compounds Bond formation Covalent bonds one way atoms stabilize their outer electron shell is to pair up with another atom in a chemical bond Atoms that share an electron are covalently bonded Ionic bonds are electrical attraction between two atoms one that has gained an electron and one that has lost one Compounds Chemical Reactions Lecture 2 Reactions between Atoms Atoms attempt to gain or loose electrons until the outer shell has 8 paired electrons Valence number of electrons to gain or loose Monovalent 1 electron Na K Cl Divalent 2 e Ca Mg O Trivalent 3 e Fe Al Tetravalent 4 e C Pentavalent 5 e P Making compounds Bond formation One way atoms stabilize their outer electron shell is to share electrons with another atom This creates a chemical bond called covalent bond Example 1 2 hydrogen atoms share electrons to form a molecule of hydrogen gas there is an equal sharing of electrons between the 2 identical H atoms This is called a non polar covalent bond Example 2 oxygen atoms have 6 electrons in their outer shell 2 of which are unpaired molecular oxygen consists of 2 atoms of O held together by 2 non polar covalent bonds since 2 electrons are shared the atoms are held together by a double bond More examples of Covalent Bonds Non polar covalent bonds electrons are shared equally Examples H H O O C H Polar covalent bonds one atom has the electron more often atom that pull the electron hardest is more electronegative Examples O H N H In the case of water 2 polarized covalent bonds the oxygen has a slight negative charge the hydrogen have a slight positive charge Ionic Bonds when an electron is stolen by one atom from another Example NaCl table salt Each atoms has one full charge and the atoms are held together by electrical attraction Hydrogen bonds electrical attraction between compounds held together by polar covalent bonds Compounds and Chemical Reactions Compounds substance composed of atoms of 2 or more different elements Molecule the smallest part of a compound retaining its properties Molecular formulas identifies the elements and the number of given atoms in a molecule Ex H2O water CH4 methane Structural formulas shows the number and arrangement of covalent bonds in a compound Shapes of molecules are quite important in understanding biology Example endorphin information carrier in brain pleasure signal bind to receptor to trigger response Morphone binds to the same receptor they do not look the same but the binding part of the molecule are identical That s why people get addicted to morphine because its binds to the pleasure receptors Molecular weight sum of atomic weights of atoms in a molecule H2O MW 1 1 16 18 CO2 MW 12 16 16 44 Mole amount of a compound equal to its molecular weight in grams H2O 1 mole 18 g CO2 1 mole 44 g One mole of a compound contains 6x10 23 atoms Solutions Most biological compounds are present as a homogenous suspension in water Solvent the dissolving medium water Solute the dissolved
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