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ChemistryChemistry--22

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Introduction: Pure Substances and

Mixtures, Elements and Compounds,

Measurements and Units

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Properties of MatterProperty – that, which can be observed or measured.

Intensive or Extensive:

Intensive - Properties independent on the amount of the matter present.

Color ,Odor; Luster; Malleability; Ductility Conductivity; Hardness; Melting/Freezing Point; Boiling Point; Density

Extensive - Properties that do depend on the amount of matter present.

Mass; Weight; Volume; Length

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Physical and Chemical ChangesPhysical change: Identity RetainedChange in the observable properties without change of substance identity Refers to material Refers to material changing changing formform but not but not in a change of composition)

Examples: Examples: melting-freezing, boiling-condensation, sublimation-

deposition)

Chemical change: Identity ChangedRefers to material transformation to a completely different new substance

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Matter consists of particles - the distance between particles and the forces that attract them define the physical state of the matter.

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A substance is a single, pure form of matter, the characteristic properties of which does not change with further purification

Mixture – combination of two or more pure substances in which each substance retains its own chemical identity.

Homogeneous mixture – composition of this mixture is uniform throughout.

Heterogeneous mixture – composition of this mixture varies throughout the mixture.

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Methods for separating the components of mixturesProcedurePhysical

property usedSeparationmethod

Pouring of solid+liquid mixture onto filter; solid trapped by filter; liquid passes trough filter

solubilityFiltration-Remove solid from liquid

Slow crystallization of solid from solution

solubilityCrystallization

Boiling off the more volatile component of a liquid mixture

volatilityDistillationPassing liquid or gaseous mixture over paper or through a column coated or packed with adsorbent

ability to adsorb to surface

Chromatography

Rotation of liquid-solid mixture at high speed in a centrifuge; solid collects at a bottom of sample tube

densityCentrifugation

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Element –the simplest type of substance with unique physical and chemical properties. An element consists of only one type of atom. It cannot be broken down into any simpler substances by physical or chemical means: Fe, P(s), H2(g), Br2(l).

Molecule - a structure that consists of two or more atoms which are chemically bound together and thus behaves as an independent unit.

The smallest (basic) unit of an element is an Atom that retains a substances chemical activity

•Compound – A substance composed of two or more elements united chemically in definite proportions, which can be broken down by using chemical techniques: NH3,NaCl, CO2

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CompoundMixture

Components can not be separated by using physical techniques

Components can be separated by using physical techniques

Composition is fixedComposition may be variable

Properties are unlike those of its components

Properties are related to those of its components

Considerable heat is produced (or absorbed) during formation

Little heat is produced during formation (accept of acids-H2O mixtures)

Differences between mixtures and compounds

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Units of MeasurementUnits of Measurement• Metric system: the set of units used for scientific

measurements.• SI Units (International System of Units): there

are seven base SI units and all other units are derived from these.

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Units of MeasurementUnits of Measurement

• We often need to express amounts that are smaller or greater than the SI units.

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Standard Conditions (IUPAC)

International Union of Pure and Applied Chemistry (IUPAC)www.iupac.org

STP „Standard temperature and pressure“p = 101 325 Pa = 1 atm, T° = 273,15 K

SATP „Standard ambient temperature and pressure“p° = 105 Pa = 1 bar, T° = 298,15 K

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Atoms, Avogadro number, mole

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Expressing the mass of an atomExpressing the mass of an atomThe mass of a hydrogen atom is 1.6727*10-27 kg.

In 1961, it was decided that C would be the element that defined the scale.

The scale of relative atomic mass of C is taken to be exactly 12 (and no units are assigned to this number). Then, the masses of all other elements are defined with respect to this scale.

Knowing the actual mass of a C atom (1.9927*10 -26kg), and the actual mass of a hydrogen atom, we can determine the relative mass of hydrogen on this scale from

1 atomic mass unit is 1 1 atomic mass unit is 1 .9927*10 -23g /12=1.6605*10/12=1.6605*10--2424ggThe mass of an atom of The mass of an atom of oxygenoxygen isis--15.995u*1.6605*1015.995u*1.6605*10--2424gg=2.6560 =2.6560 1010--2323ggThe mass of a The mass of a uraniumuranium=3.9029 *10=3.9029 *10--2222gg

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Avogadro's number and the moleAvogadro's number and the mole

Avogadro's number: Avogadro's number: establishes a link between the establishes a link between the mass of macroscopic amounts of matter that we mass of macroscopic amounts of matter that we ordinarily deal with and the masses of individual ordinarily deal with and the masses of individual atomsatoms

12g/ 1 12g/ 1 .9927*10 -23g= 6.02 x 106.02 x 1023 23 atomsatoms

The mole is the The mole is the amount of substanceamount of substance of a system, of a system, which contains as many elementary particles as there which contains as many elementary particles as there are atoms in 12 gram of carbonare atoms in 12 gram of carbon--12.12.1 mole= 12g C1 mole= 12g C

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Mass Moles Conversion

Moles to Mass

moles • grams = grams1 mole

Molar mass

Mass to Moles

grams • 1 mole = molesgrams

1 / Molar mass

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Properties Properties of the Three Key Subatomic Particles

Charge Mass

Relative

1+

0

1-

Absolute(C)*

+1.60218x10-19

0

-1.60218x10-19

Relative(amu)†

1.00727

1.00866

0.00054858

Absolute(g)

1.67262x10-24

1.67493x10-24

9.10939x10-28

Location in the Atom

Nucleus

Outside Nucleus

Nucleus

Name(Symbol)

Electron (e-)

Neutron (n0)

Proton (p+)

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• Electron configuration– Ground state (all electrons in lowest energy states)– Core electrons (electrons in inner shells, non-

bonding)– Valence electrons (electrons in outermost shell,

bonding-The outermost electrons of an atom determine its chemical and electrical properties.

• Stable electronic configuration, valence shell is filled

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Atomic Numbers, and Mass NumbersAtomic Numbers, and Mass Numbers

Atomic number (Z) = number of protons in the nucleus.

Mass number (A) = total number of protons and neutrons in the nucleus.

Cexample

XAZ

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:

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Effective nuclear charge - The charge experienced by an electron in a many-electron atom

Zeff is lower than actual nuclear charge.

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Isotope: Atom of an element with fixed number of protons, but varying number of neutrons (the same atomic number, but different atomic mass)

GreekGreek--equal placeequal place

• In this series of elements, the mass number (A) varies but theatomic number (Z) is constant.

• This means that we are looking at a series of isotopes.

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The Periodic Law: The Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.

-Mendeleev arranged the elements in order of increasing atomic mass (A) to reflect the trends in chemical and physical properties.

-Modern periodic table (Henry Moseley):arrange elements in order of increasing atomic number (Z). XA

Z

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Physical propertiesPhysical propertiesMetals Nonmetals

Opaque as thin sheet Transparent as a thin sheet

Good electricalconductors andheat conductors.

Poor conductors of heat and electricity

Malleable - can be beaten into thin sheets Brittle - if a solid

Ductile - can be stretched into wire Nonductile

Possess metallic luster Do not possess metallic luster

Solid at room temperature(except Hg)

Solids, liquids or gases at room temperature

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Chemical propertiesChemical properties

Metals NonmetalsUsually have 1-3 electrons in their outer shell Usually have 4-8 electrons in

their outer shellLose their valenceelectrons easily Gain or share valence

electrons easily.Form oxides that are basic Form oxides that are acidic

Are good reducing agents Are good oxidizing agents

Have lower electronegativities

Have higher electronegativities

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Group I: Alkali MetalsGroup I: Alkali Metals• Lithium, Sodium and Potassium are solids• Shiny surfaces when freshly cut• Very soft metals• All have the same s1 valence electrons• All easily lose 1 electron to give M + Ion.• Reactive with oxygen, chlorine & water

Group II: Alkaline Earth MetalGroup II: Alkaline Earth Metal

• All are solids at room temperature• All metals have shiny surfaces• Much harder than group I metals• All have the same s2 valence electrons• Lose 2 electrons to give M2+ ion• Less reactive than group I metals

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Group VI: Oxygen GroupGroup VI: Oxygen Group• Oxygen is a gas, all others are solids with increasing metallic

character.• Tellurium is a metalloid and Polonium is a metal• All have same s2p4 valence electrons• All easily gain 2 electron to give X2- ion• Can form 2 allotropes O2 and O3.• Attracts electrons from most other elements.

Group VII: HalogensGroup VII: HalogensGroup VII: Halogens• Fluorine and Chlorine are gases, Bromine is a liquid, Iodine is a

solid• Chlorine, Bromine and Iodine are colored• All are non-metals• All have same s2p5 valence electrons• All easily gain 1 electron to give X- ion• Reactive with many elements.

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HydrogenHydrogen• Gas at room temperature

• Has a 1s1 electron configuration

• Does not belong to a group

• High Ionization energy (1312kJ/mol)

• Can lose or gain 1 electron which means its properties can be similar to a metal (Li) or a non-metal (F)

Group VIII: Noble GasesGroup VIII: Noble GasesGroup VIII: Noble Gases• All are gases• All are non-metals• All are monatomic• All have same s2p6 valence electrons• Very non-reactive.

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•The 38 elements in groups 3 through 12 of theperiodic table are called "transition metals".

•As with all metals, the transition elements are both ductile and malleable, and conduct electricity and heat.

•Their valence electrons, are present in more than one shell. This is the reason why they often exhibitseveral common oxidation states.

•There are 3 noteworthy elements in the transition metals family: Fe, Co, and Ni, and they are the only elements known to produce a magnetic field.

Group III-XII: Transition MetalsGroup III-XII: Transition Metals

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Atomic Size

Atomic radius Atomic radius -- distance from the center of an atom's distance from the center of an atom's nucleus to its outermost electrons. Since no distinct nucleus to its outermost electrons. Since no distinct boundary, we can think of atomic radius as half the boundary, we can think of atomic radius as half the distance between the two nuclei of bonded atomsdistance between the two nuclei of bonded atoms

Remember: large number of elements are found under ordinary conditions as diatomic molecules—N2, O2, etc.—polyatomic molecules—P4, S8, etc.—or solid metals. Here we are considering only free atoms, often produced at high temperatures only, and in the gas phase only

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Periodic Trends in Atomic size and Ionization Energy