Atoms & Elements

							Atoms & Elements
What is Chemistry?

• The study of matter of matter
  and its changes
What does a chemist
do?
• Chemists analyze substances
• Chemists create or synthesize
  new substances
• Chemists create models and
  test the power of theories
• Chemists measure the physical
  properties of substances
Areas of chemistry

•   Analytical chemistry
•   Organic chemistry
•   Inorganic chemistry
•   Physical chemistry
•   biochemistry
Careers in chemistry

•   Quality control chemist
•   Industrial research chemist
•   Forensic chemist
•   Environmental chemist
•   Sales representative
•   Chemical educator
Scientific Method

• Consists of three parts:
• Observation
• Explanation through the
  creation of a theoretical model
• Testing the model
Observations

• A statement(s) that describe
  what we see, touch, feel, smell,
  or taste (the five senses)
Conclusion

• A statement as to what one
  thinks about a series of
  observations
Data

• Facts that are learned by
  observing some physical,
  chemical or biological system
Scientific Law

• A broad generalization, based
  on the results of many
  experiments
• Scientific laws are expressed in
  terms of mathematical
  equations: (Examples: E = mc2,
  PV = nRT , PV= C)
Classification of Matter

• Matter is anything that has
  mass and occupies space
• Matter can be classified as
  elements, compounds, or
  mixtures
Elements

• Substances that cannot be
  decomposed further by ordinary
  chemical means.
• All elements can be identified
  by a chemical symbol
Elements (cont.)

• The first letter is always
  capitalized
• The second letter (if there is
  one) is always lowercase
Compounds

• A substance that is composed
  of two or more different
  elements in which elements are
  always combined in a fixed ratio
Examples of compounds

•   Carbon dioxide (CO2)
•   Water (H2O)
•   Ammonia (NH3)
•   Glucose (C6H12O6)
•   Sodium chloride (NaCl)
Mixtures

• Materials that have variable
  composition
• Two types of mixtures: a)
  homogeneous
 and b) heterogeneous
Homogeneous Mixtures

• Homogeneous mixtures have
  properties that are identical
  throughout the sample
• All solutions are considered to
  be homogeneous mixtures
Examples of
homogeneous mixtures
• Air (a mixture of gases)
• Alloys (brass, bronze, sterling
  silver, steel)
• Rubbing alcohol (isopropyl
  alcohol and water)
• Saltwater
Heterogeneous Mixtures

• Heterogeneous mixtures
  consists of regions (phases)
  which are not uniform.
Examples of
Heterogeneous Mixtures
•   Oil & water
•   Salads
•   Soups
•   Blood
•   Milk
Physical and Chemical
Changes
• Physical change: A change in
  which no change in the
  composition occurs. No nes
  substances are formed
• Chemical change: A change in
  which the composition of the
  substance is changed
Examples of physical
changes
•   Ice melting
•   Water boiling
•   Dissolving sugar in water
•   Alcohol changing into a vapor
Examples of chemical
changes
•   Sugar fermenting into alcohol
•   Iron rusting
•   Silver tarnishing
•   Butter turning rancid
Properties of Matter

• Physical Properties: Properties
  which does not involve a
  change in chemical composition
  (Examples: density, melting
  point, boiling point, solubility,
  malleability, etc.)
Chemical properties

• Properties which describe a
  chemical change which takes
  place
• Examples: Sugar decomposes
  when heated, iron changes to
  rust when exposed to moist air
Extensive Properties

• A property that depends on the
  size of the sample
• Examples: Volume, mass, and
  length
Intensive properties

• Properties that are independent
  of sample size
Examples of Intensive
Properties
•   Color
•   Melting point
•   Boiling point
•   Density
•   Electrical conductivity
• Intensive properties are better
  in identifying than extensive
  properties
States of Matter

• Solid: Definite shape & volume
• Liquid: Definite volume, but
  indefinite shape
• Gas: Indefinite shape & volume
Law of conservation of
mass
• States that matter cannot be
  created nor destroyed
• Mass is conserved
Law of definite
proportions
• States that in a given chemical
  compound, elements are always
  combined in the same
  proportions by mass
Dalton’s Atomic Theory

• Matter consists of tiny particles
  called atoms
• Atoms are indestructible
• In any sample of a pure
  element, all atoms are identical
  in terms of mass and other
  properties
Dalton’s atomic theory
(cont.)
• The atoms of different elements
  differ in mass and other
  properties
• When atoms of different
  combine to form compounds,
  new and more complex
  particles form
Law of multiple
proportions
• Whenever two elements form
  more than one compound, the
  different masses of one element
  that combine with the same
  mass of the other element are
  in the ratio of small whole
  numbers.
Law of Multiple
Proportions (cont)
• Example: Sulfur can react with
  oxygen to form two different
  compounds:
   SO2
   SO3
Subatomic Particles

• Consists of protons, neutrons,
  and electrons
• Protons possess a positive
  charge
• Electrons possess a negative
  charge
• Neutrons possess a neutral (no)
  charge
• Protons and neutrons are
  located in the nucleus of the
  atoms
• Electrons move about the
  nucleus
Isotopes

• Atoms that have the same
  number of protons, but different
  number of neutrons
Atomic number & Mass
number
• Atomic number : number of
  protons
• Mass number: number of
  protons & neutrons
Atomic mass

• Weighed average of all isotopes
  that compose that element
• Units are expressed in atomic
  mass units (amu) for each atom
• Carbon-12 is used as the
  standard
Atomic Mass Unit

• Symbolized as u
• 1/12 the mass of the carbon-12
  isotope
• Average atomic masses can be
  determined from isotopic
  abundances
The periodic table

• Developed by Mendeleev in
  1871
• His table arranged elements
  based on increasing atomic
  mass
• Modern periodic table arrange
  elements based on increasing
  atomic number
• Horizontal rows are called
  periods
• Vertical rows are called groups
  or families
Groups & families of
elements
• Representative elements:
  (Groups IA- VIIIA)
• Alkali metals (Group IA)
• Alkaline earth metals (Group
  IIA)
• Halogens (Group VIIA)
• Noble gases (Group VIIIA)
• Transition elements (B groups)
• Inner transition elements
   a) lanthanides (58-71)
   b) actinides (89-103)
Characteristics of
Metals
•   Solid (except Hg)
•   Exhibit a luster (shiny)
•   Ductile
•   Malleable
•   Good conductors of
    heat/electricity
Characteristics of
nonmetals
• Solids, gases, and one liquid
• Solids are brittle
• Poor conductors of
  electricity/heat
• Not malleable
• Not ductile
Metalloids

• Possess characteristics
  between those of metals and
  nonmetals
• Tend to serve as
  semiconductors
• Examples: silicon, boron,
  germanium, tellurium, etc.