BASIC CHEMISTRY Becky Sheridan

What is stuff made of? Matter: –Occupies space & has mass Elements: –Pure chem. substance that can’t be broken into other substances –CHONPS –CHON 96.3% of mass of most living things Atom: –Smallest unit of an element

ATOMS The smallest particle of an element that can exist and still have the properties of that element. An atom has many subatomic particles ParticleChargeLocationMass Proton+Nucleus1 amu * NeutronNNucleus1 amu Electron- Cloud 0 ** Atomic mass unit or Dalton ** The mass of an e- is so small it’s negligible.

Electrons Move around the nucleus in specific energy levels/energy clouds. Their exact location varies at any given time. Have a negative charge Repel one another Number of e-’s is equal to the #of protons. Neutral

Protons Protons determine the identity of an element. Positive charge Located in the nucleus Atomic Number = # protons

Neutrons Located in the nucleus Neutral Charge Atomic Mass = # p and # n To determine the # of neutrons, subtract the atomic number from the atomic mass. Example: Carbon 12 – 6 = 6 neutrons

Elements A substance which cannot be split into simpler substances by a chemical rxt. A substance consisting of only one type of atom Represented by a symbol Usually 1st letter of the English name Sometimes the 1 st and 2 nd letters 6 C 12.01

Elements Are listed on the Periodic Table Dimitri Mendele’ev 1869 Arranged in order of their atomic #’s Table is divided into Groups and Periods The atomic number and atomic mass are given for each element. Example: 6 C Atomic # Atomic Mass Element

Groups Vertical Column Numbered 1-8 All elements of same group have the same # of e-’s in their valence shell & have similar chemical properties Atomic # increases by 1 from left to right Example: H, Li, Na, K, Rb, Cs, Fr All have 1 e- in valence (outer) shell

Periods Is a horizontal row of elements There are 7 periods Elements in a period have the same # of energy levels Example: H and He are in period 1 They have 1 energy level

Isotopes The atomic number is the same Atoms of the same element that have different mass numbers Examples: Protons Neutrons Carbon-126 protons 6 neutrons -99% of all C atoms Carbon-136 protons 7 neutrons 1% Carbon-146 protons8 neutrons -Trace amounts

Ions An electrically charged element, formed when an atom loses or gains electrons Two types: Anions: negative charge Cations: positive charge

Cations Atom that loses electrons Positively charged ion Elements in Groups 1, 2, and 3 tend to lose electrons Metallic elements tend to form positive ions Example: Ca Lose 2 electrons +2 charge

Anion Atom that gains electrons Negatively charged ion Elements in groups 5, 6, and 7 tend to gain electrons Nonmetallic elements tend to form anions Example: Cl Gain 1 electron -1 charge

Ionic Compounds Metals react with nonmetals forming ionic compounds Salts Held together by electrostatic forces Ex. + attracted to – Most are crystalline solids at room temperature When dissolved in water they conduct electricity Ex. Sodium Chloride or Table Salt Na++ Cl- Dissociate(break apart) in water, producing free ions

Electrolyte A solution that conducts electricity. Term for salts, specifically ions. The term electrolyte means that this ion is electrically-charged and moves to either a negative (cathode) or positive (anode) electrode Ions that move to the cathode (cations) are positively charged Ions that move to the anode (anions) are negatively charged

ELECTROLYTES Example Your body fluids -- blood, plasma, interstitial fluid (fluid between cells) -- are like seawater and have a high concentration of sodium chloride (table salt, or NaCl). The electrolytes in sodium chloride are: Sodium ion (Na + ) or a cation Chloride ion (Cl - ) or an anion

Important Electrolytes Sodium (Na + ) Potassium (K + ) Chloride (Cl - ) Magnesium (Mg 2+ ) Calcium (Ca 2+ ) Phosphate (PO 4 2- ) Bicarbonate (HCO 3 - ) Sulfate (SO 4 2- )

Ionic Bonds & Compounds Review Forces that hold two oppositely charged ions together. Electrostatic Forces Ionic bonds tend to be stronger than other types of chemical bonds. Occur between metals and non- metals. Dissociate in water Crystalline solid Conduct electricity

Ionic Bonding

Covalent Bonds Bonds formed when atoms share electrons Atoms with 4 or 5 e-’s tend to share Each e- spends part of its time around one nucleus and then around the other nucleus. Sharing e-’s completes the valence shell

Covalent Bonds Bonds between non-metals Poor conductors of electricity Do not dissociate easily in water Two Types: Polar: Unequal Sharing Non-Polar: Equal Sharing

Non-Polar Covalent Bonds Equal sharing of e-’s Small difference or the same electronegativity Diatomic (Two atoms combine) H and HH 2 F and FF 2 Electronegativity same

Non-Polar Covalent Bonds Pull on one another equal Electrons spend equal amount of time around each nucleus. Do not dissolve in water Hydrophobic

Polar Covalent Bonds Unequal sharing of electrons One atom “pulls” on e-’s harder than the other One atom has a higher electronegativity than the other. Partial charges result around each end or pole

Polar Covalent Bonds Polar e-’s spend more time around one end or the other. Dissolve in water Hydrophilic Example: Water

Water Molecule Partial Charges

Electronegativity The ability of an atom to compete for e- with the other atom to which it is bonded (Scale devised by L. Pauling varies from 0 - 4). Difference in electronegativity is usually less than 1.7 O and F are the most electronegative elements. Atom ONSCHPF Electronegativity

Examples: H-H2.1 – 2.1 = 0 Diatomic Non-Polar H-F 4 – 2.1 = 1.8 Polar

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