Introduction: Pure Substances and. Mixtures, Elements and Compounds, Measurements and Units

Transcription

1 1 Chemistry-2

2 Introduction: Pure Substances and Mixtures, Elements and Compounds, Measurements and Units 2

3 Properties of Matter Property 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 3

4 Physical and Chemical Changes Physical change: Identity Retained Change in the observable properties without change of substance identity Refers to material changing form but not in a change of composition) Examples: melting-freezing, boiling-condensation, sublimationdeposition) Chemical change: Identity Changed Refers to material transformation to a completely different new substance 4

5 Matter consists of particles - the distance between particles and the forces that attract them define the physical state of the matter. 5

6 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. 6

7 Methods for separating the components of mixtures Separation method Physical property used Procedure Filtration- Remove solid from liquid solubility Pouring of solid+liquid mixture onto filter; solid trapped by filter; liquid passes trough filter Crystallization solubility Slow crystallization of solid from solution Distillation volatility Boiling off the more volatile component of a liquid mixture Chromatography ability to adsorb to surface Passing liquid or gaseous mixture over paper or through a column coated or packed with adsorbent 7 Centrifugation density Rotation of liquid-solid mixture at high speed in a centrifuge; solid collects at a bottom of sample tube

8 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), H 2 (g), Br 2 (l). Molecule - a structure that consists of two or more atoms which are chemically bound together and thus behaves as an independent unit. 8 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: NH 3, NaCl, CO 2

9 Differences between mixtures and compounds Mixture Components can be separated by using physical techniques Composition may be variable Properties are related to those of its components Little heat is produced during formation (accept of acids- H 2 O mixtures) Compound Components can not be separated by using physical techniques Composition is fixed Properties are unlike those of its components Considerable heat is produced (or absorbed) during formation 9

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11 Units 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. 11

12 Units of Measurement We often need to express amounts that are smaller or greater than the SI units. 12

13 Standard Conditions (IUPAC) International Union of Pure and Applied Chemistry (IUPAC) STP Standard temperature and pressure p = Pa = 1 atm, T = 273,15 K SATP Standard ambient temperature and pressure p = 10 5 Pa = 1 bar, T = 298,15 K 13

14 Atoms, Avogadro number, mole 14

15 Expressing the mass of an atom The mass of a hydrogen atom is *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*10-26 kg), and the actual mass of a hydrogen atom, we can determine the relative mass of hydrogen on this scale from 15 1 atomic mass unit is *10-23 g /12=1.6605*10-24 g The mass of an atom of oxygen is u*1.6605*10-24 g= The mass of a uranium= *10-22 g g

16 Avogadro's number and the mole Avogadro's number: establishes a link between the mass of macroscopic amounts of matter that we ordinarily deal with and the masses of individual atoms 12g/ *10-23 g= 6.02 x atoms The mole is the amount of substance of a system, which contains as many elementary particles as there are atoms in 12 gram of carbon mole= 12g C 16

17 Mass Moles Conversion Moles to Mass moles grams = grams 1 mole Mass to Moles grams 1 mole = moles grams Molar mass 1 / Molar mass 17

18 Properties of the Three Key Subatomic Particles Name(Symbol) Charge Relative Absolute(C)* Relative(amu) Mass Absolute(g) Location in the Atom Proton (p + ) x x10-24 Nucleus Neutron (n 0 ) x10-24 Nucleus Electron (e - ) x x10-28 Outside Nucleus 18

19 Electron configuration Ground state (all electrons in lowest energy states) Core electrons (electrons in inner shells, nonbonding) 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 19

20 Atomic 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. A Z X example : 12 6 C 20

21 Effective nuclear charge - The charge experienced by an electron in a many-electron atom Z eff is lower than actual nuclear charge. 21

22 Isotope: Atom of an element with fixed number of protons, but varying number of neutrons (the same atomic number, but different atomic mass) Greek-equal equal place 22 In this series of elements, the mass number (A) varies but the atomic number (Z) is constant. This means that we are looking at a series of isotopes.

23 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. 23 -Modern periodic table (Henry Moseley): arrange elements in order of increasing atomic number (Z). A Z X

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25 Metals Good electrical conductors and heat conductors. Malleable - can be beaten into thin sheets Physical properties Nonmetals Poor conductors of heat and electricity Brittle - if a solid 25 Ductile - can be stretched into wire Possess metallic luster Opaque as thin sheet Solid at room temperature (except Hg) Nonductile Do not possess metallic luster Transparent as a thin sheet Solids, liquids or gases at room temperature

26 Chemical properties Metals Usually have 1-3 electrons in their outer shell Lose their valence electrons easily Form oxides that are basic Are good reducing agents Have lower electronegativities Nonmetals Usually have 4-8 electrons in their outer shell Gain or share valence electrons easily. Form oxides that are acidic Are good oxidizing agents Have higher electronegativities 26

27 Group I: Alkali Metals Lithium, Sodium and Potassium are solids Shiny surfaces when freshly cut Very soft metals All have the same s 1 valence electrons All easily lose 1 electron to give M + Ion. Reactive with oxygen, chlorine & water Group 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 s 2 valence electrons Lose 2 electrons to give M 2+ ion Less reactive than group I metals 27

28 Group 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 s 2 p 4 valence electrons All easily gain 2 electron to give X 2- ion Can form 2 allotropes O 2 and O 3. Attracts electrons from most other elements. Group 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 s 2 p 5 valence electrons All easily gain 1 electron to give X - ion Reactive with many elements. 28

29 Hydrogen Gas at room temperature Has a 1s 1 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 Gases All are gases All are non-metals All are monatomic All have same s 2 p 6 valence electrons Very non-reactive. 29

30 Group III-XII: Transition Metals The 38 elements in groups 3 through 12 of the periodic 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 exhibit several 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. 30

31 Atomic Size Atomic radius - distance from the center of an atom's nucleus to its outermost electrons. Since no distinct boundary, we can think of atomic radius as half the distance between the two nuclei of bonded atoms Remember: large number of elements are found under ordinary conditions as diatomic molecules N 2, O 2, etc. polyatomic molecules P 4, S 8, etc. or solid metals. Here we are considering only free atoms, often produced at high temperatures only, and in the gas phase only 31

32 32 Periodic Trends in Atomic size and Ionization Energy