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Chem Midterm Review

Chem Midterm Review - What is chemistry The study of matter...

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What is chemistry? The study of matter and the changes that matter undergoes o Matter is made up of almost infinitely small building blocks called atoms Atoms combine together to form a compound o Classification of matter Is it uniform throughout? Yes: homogeneous o Can it be separated by physical means? Yes: homogeneous mixture (solution) No: pure substance Can it be decomposed into other substances? o Yes: compound o No: element No: heterogeneous Element – cannot be broken down into simpler substances Compound – fixed composition, but can be broken down into elements Mixture – variable composition of elements and/or compound Molecules – combination of a fixed number of atoms held together in a certain geometric arrangement Chemical formulas – symbolic representations of the elementary composition of chemical compounds (ex. Nitrogen: N 2 ; water: H 2 O) Chemical reactions – atoms are rearranged in different compounds: reactants are transformed into products o Carbon + oxygen carbon dioxide o C + O 2 CO 2 Law of conservation of mass – in a chemical reaction mass is conserved o CH 4 + 2O 2 CO 2 + 2H 2 O Characteristics of chemical reactions Always conserved o Number of atoms in reactants = number of atoms in products o Identity of atoms in reactants = identity of atoms in products o Total mass of reactants = total mass of products Atomic Structure Modern view of the atom : positively charged nucleus , surrounded by negatively charged electrons Nucleus : contains two types of subatomic particles: o Protons : positively charged (+) o Neutrons : not charged Protons and neutrons make up nearly all of the mass of an atom, but they occupy only a very small percentage of its total volume In an electrically neutral atom, the number of electrons equals the number of protons Lewis Dot Representation Hydrogen – H .
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Helium – He: Electronic Arrangements in Atoms Number above the atomic symbol is the number of electrons in a neutral atom. This is the same as the atomic number , which gives the number of protons Periodic Table and Atomic Structure Elements are arranged in order of increasing atomic number (number of protons) Elements with similar chemical properties fall in the same columns (groups) (same number of valence electrons) Elements in the same row (period) have the same number of core electrons and same number of energy levels Chemical properties vary in a regular way with increasing atomic number (periodicity) Chemical Bonding Octet rule : atoms tend to gain, lose, or share electron until they are surrounded by eight valence
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