The Structure of Matter: The Structure of Matter: Compounds & MoleculesCompounds & Molecules

•Chemical bondChemical bond - the attractive - the attractive force that holds atoms or ions force that holds atoms or ions togethertogether

•Chemical structureChemical structure – the – the arrangement of bonded atoms arrangement of bonded atoms or ions within a substanceor ions within a substance

Compounds & Molecules 2Compounds & Molecules 2

•Bond lengthBond length – average – average distance between nuclei of distance between nuclei of two bonded atomstwo bonded atoms

•Bond angleBond angle – angle made – angle made by 2 bonds to the same by 2 bonds to the same atomatom

Compounds & Molecules 3Compounds & Molecules 3

•What’s the difference between What’s the difference between compounds and mixtures?compounds and mixtures?

•Figure out the relative #s of Figure out the relative #s of atoms or ions in a compound atoms or ions in a compound from its chemical formula.from its chemical formula.

Compounds Vs. Mixtures 1Compounds Vs. Mixtures 1

•Compounds have very Compounds have very different properties from the different properties from the elements that make them. elements that make them.

•Here, elements lose solo Here, elements lose solo properties when they bond properties when they bond together.together.

Compounds Vs. Mixtures 2Compounds Vs. Mixtures 2

•Compounds = Compounds = same substances same substances or different onesor different ones that are that are chemically bonded to each other chemically bonded to each other like Olike O22 or the H’s & O’s in two or the H’s & O’s in two molecules of water, 2Hmolecules of water, 2H22O. O.

•Reactions that form these Reactions that form these involve breaking of bonds & involve breaking of bonds & rearrangement of atoms into rearrangement of atoms into new bonds.new bonds.

Compounds Vs. Mixtures 3Compounds Vs. Mixtures 3

•Mixtures = Mixtures = differentdifferent substances that substances that are just placed together not bonded are just placed together not bonded and still keep their individual and still keep their individual properties.properties.

•Compounds have chemical formulas Compounds have chemical formulas which show the types & numbers of which show the types & numbers of atoms or ions that make up their atoms or ions that make up their simplest units.simplest units.

Compounds Vs. Mixtures 4Compounds Vs. Mixtures 4

•Compounds always have Compounds always have the same elements in the the same elements in the same combinations.same combinations.

•Consider CConsider C66HH1212OO66 for for glucose, a product of glucose, a product of photosynthesis.photosynthesis.

Compounds Vs. Mixtures 5Compounds Vs. Mixtures 5

•Anywhere that one finds a Anywhere that one finds a molecule of glucose in the molecule of glucose in the universe, this compound will universe, this compound will have 6 carbon, 12 hydrogen have 6 carbon, 12 hydrogen & 6 oxygen atoms all & 6 oxygen atoms all chemically bonded together.chemically bonded together.

Chemical Structure: Chemical Structure: Bonding Within Bonding Within CompoundsCompounds

•Chemical formulas don’t Chemical formulas don’t show how atoms are show how atoms are connectedconnected

•In other words, they do not In other words, they do not reveal bond angles & bond reveal bond angles & bond lengths between atoms.lengths between atoms.

Bonding Within Compounds Bonding Within Compounds 22

•However, However, modelsmodels do show do show bond lengths and angles.bond lengths and angles.

•Structural formulasStructural formulas can can show bond angles too but show bond angles too but not bond lengths. not bond lengths.

Models of Compounds 3Models of Compounds 3

•Ball-and-stickBall-and-stick models give models give an idea of bond lengths an idea of bond lengths and bond angles.and bond angles.

•Space filling models show Space filling models show the space that bonded the space that bonded atoms occupy well.atoms occupy well.

Models of Compounds 4Models of Compounds 4

•However, space filling However, space filling models make it difficult to models make it difficult to “see” the bond lengths “see” the bond lengths and angles between the and angles between the atoms in a compound.atoms in a compound.

Structure Affects Structure Affects Properties 1Properties 1•Network structure includes the Network structure includes the

same bond angles throughout same bond angles throughout the compound and multiple the compound and multiple bonds on repeating centers. bonds on repeating centers.

•This results in strong solids with This results in strong solids with unusually strong bonds that take unusually strong bonds that take more energy to break.more energy to break.

Structure Affects Properties Structure Affects Properties 22•For example in quartz, 4 oxygen For example in quartz, 4 oxygen

atoms bond each silicon atom at atoms bond each silicon atom at 109.5109.5˚̊ angles. angles.

•High melting points (mp) & boiling High melting points (mp) & boiling points (bp) result from network points (bp) result from network structures b/c it takes more heat structures b/c it takes more heat energy to break stronger bonds.energy to break stronger bonds.

Structure Affects Properties Structure Affects Properties 33

•Networks can be made of Networks can be made of bonded positive and negative bonded positive and negative ions in cube shaped crystals.ions in cube shaped crystals.

•Molecular or covalent Molecular or covalent compounds have weaker bonds compounds have weaker bonds & as a result lower melting & & as a result lower melting & boiling points.boiling points.

Structure Affects Properties Structure Affects Properties 44

•IonicIonic compounds – bonds compounds – bonds between between ionsions where these where these charged atomscharged atoms have have given given away or takenaway or taken electrons. electrons.

•CovalentCovalent compounds – bonds compounds – bonds between between atomsatoms where these where these atomsatoms shareshare electrons. electrons.

Structure Affects Structure Affects Properties 5Properties 5•How do weaker bonds cause How do weaker bonds cause

lower mp and bp?lower mp and bp?

•Different structures in Different structures in molecular compounds result molecular compounds result in different mp and bp even in different mp and bp even among among groupgrouped compounds.ed compounds.

Structure Affects Structure Affects Properties 6Properties 6• Consider Table 4-2 on page 113 and Consider Table 4-2 on page 113 and

Figure 4-8 on page 114.Figure 4-8 on page 114.• Structure affects even the strength of Structure affects even the strength of

attractions beween molecules.attractions beween molecules.• For example, intermolecular For example, intermolecular

attraction between molecules of Hattraction between molecules of H220 0 is stronger than attraction between is stronger than attraction between those of Hthose of H22S, dihydrogen sulfide.S, dihydrogen sulfide.

Structure Affects Structure Affects Properties 7Properties 7•What do the decreasing mp and bp What do the decreasing mp and bp

for sugar (Cfor sugar (C1212HH2222OO1111), H), H220 & H0 & H22S in S in this order tell us about their relative this order tell us about their relative attractions for each other? attractions for each other?

•Rank them in order of least to Rank them in order of least to greatest intermolecular attraction.greatest intermolecular attraction.

Structure Affects Structure Affects Properties 8Properties 8•Notice that sugar & water have Notice that sugar & water have

very different stuctures w/ very different stuctures w/ expectedly different properties.expectedly different properties.

•However, water & dihydrogen However, water & dihydrogen sul-fide have more similar sul-fide have more similar structures than properties. Why structures than properties. Why is this?is this?

Structure Affects Structure Affects Properties 9Properties 9

•Hydrogen bondingHydrogen bonding – extra – extra strong intermolecular strong intermolecular attractions between attractions between hydrogen and oxygen hydrogen and oxygen atoms in nearby atoms in nearby compounds.compounds.