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p. 144-156. Chemical Bonding. Remember…. There are two kinds of pure substances. Elements Compounds. Elements. Substance that cannot be separated or broken down into simpler substances by chemical means. Ex’s- any box on the periodic table Made of only 1 type of atom
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p. 144-156 Chemical Bonding
Remember….There are two kinds of pure substances Elements Compounds
Elements • Substance that cannot be separated or broken down into simpler substances by chemical means. • Ex’s- any box on the periodic table • Made of only 1 type of atom • The smallest unit of an element that maintains the properties of that element • HUH?
The smallest unit of an element that maintains the properties of that element??? • The element sodium has certain properties • 11 protons, 11 electrons, etc and that determines properties like boiling point, reactivity, etc.
Compounds cont… • Substance made of atoms of 2 or more different elements that are CHEMICALLY combined. • Elements are combined in a definite way and this changes their properties Na- lethal if ingested Cl- lethal if ingested NaCl- table salt
Molecules • Two or more atoms bonded together… • They can be two of the same element or two different elements- this would be a compound • All compounds are molecules, but not all molecules are compounds. • Ex- O2, NaCl, etc.
Compounds Molecules made by two or more elements bonded together -always in a definite ratio Elements Molecules made of just one element What is a pure substance? NaCl (sodium chloride/salt) Na (sodium)
Compound/Molecule • Chemical combination of 2 or more elements. • Properties of the compound are unlike those of the elements that make it. • Represented by a formula that gives the ratio of atoms of the elements. • Ex- The formula NaCl tells you that salt is a compound made of one Na and one Cl. • The ratio is then 1:1
Chemical Bond • Force which holds atoms together. • 3 Types: • Metallic • Ionic • Covalent • Polar • Nonpolar
Metallic Bonds • Formed between 2 or more metal atoms (elements). • Valence electrons overlap. • The electrons are free to move about all the atoms; therefore, they are good conductors of electricity. • Ex) Mg, Cu, Fe, etc. form these types of bonds
Ionic Bonds(formed in ionic compounds) • IONS are the basic unit (atom with a charge). • CATION = ion that has a + charge (lost e-‘s) • ANION = ion that has a – charge (gained e-‘s)
How are these ions made? • Can you mess with protons? • Would messing with neutrons do anything to the charge? • What must you mess with??? • What charge does an electron have? • So what would happen to the atom if they LOSE one? Would they get more positive or more negative overall???
How do ions stick together? • Force of attraction between oppositely charged ions. • (anion & cation) • Ionic bonds are very strong bonds. • Formed between metal & nonmetal atoms (elements). • Electronegativity difference between the atoms is 1.7 or greater. (see table on last page of notes) • Ex) Na & Cl
Ionic Compounds: • pack into a pattern (crystal; lattice) • have very high melting points.
Ionic Compound Cont… • Dissolve in water (H2O), and ions are then free to move (dissociate). • Conduct electric current.
Covalent Bonds(formed in molecular/covalent compounds) • Atoms are the basic unit. • Covalent bonds are firm, but molecules not strongly held together. • Force between atoms that share electrons.
Kinds of Covalent Bonds • Can share different number of electrons: • Single- share ONE pair of electrons • Double- share TWO pair of electrons • Triple- share THREE pairs of electrons • Can be polar covalent or nonpolar covalent bonds.
Nonpolar Covalent bonds: • Electrons are shared equally in the bond. • Does not have (+) and (-) end to the bond. • Formed between 2 or more of the same nonmetal. • Electronegativity difference between the atoms (elements) is 0. (see table on last page of notes) • Ex) Cl & Cl
Polar Covalent bonds: • Electrons are NOT shared equally in the bond. • Has a (+) and (-) end to the bond. • Formed between 2 different nonmetals. • Electronegativity difference between the atoms (elements) is 0.1-1.6 (see table on last page of notes) • Ex) H & O C & O
How do you know which type of bond will form? Use two rules: • Calculation using electronegativity values on a periodic table: (Note: if they are both/all metals, automatically, it is a metallic bond!) • Subtract the values of the 2 elements (larger minus smaller) • If difference is: 0= nonpolar covalent bond 0.1-1.6= polar covalent bond 1.7 & up= ionic bond
Electronegativity Differences summary… If difference is: 0.1-1.6 Electronegativities are not different enough to steal the electron away, but there will be a “bully” who hugs the electrons closer If differenc is 1.7 & up Electronegativities are so great that one atom will steal the eletron away 0 difference Electronegativities are the same, so the atoms will share nicely
A second way… “rule of thumb” • 2) Periodic table/metal, nonmetal rule (Rule of thumb): • Metal and Metal = metallic bond • Metal and nonmetal = ionic bond • Nonmetal and nonmetal = covalent • All same nonmetal = nonpolar covalent bond • Different nonmetals = polar covalent bond
Rule of thumb summary… Two different nonmetals A metal with a nonmetal Two Metals Both the same metal
Covalent/ Molecular Compounds: • Not packed into a pattern. • Have low melting points. • May not dissolve in water (H2O), but some can. • Do not conduct electricity; do not dissociate.
