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Chapter 3. Atoms and Elements Classifying Matter Elements and Symbols Periodic Table Atomic Structure Atomic Mass Electronic Structure Periodic Trends. Classification of Matter. Pure Substance = matter that has a fixed or definite composition.

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chapter 3
Chapter 3
  • Atoms and Elements
    • Classifying Matter
    • Elements and Symbols
    • Periodic Table
    • Atomic Structure
    • Atomic Mass
    • Electronic Structure
    • Periodic Trends
classification of matter
Classification of Matter
  • Pure Substance = matter that has a fixed or definite composition.
    • Both elements and compounds are examples of pure substances.
classification of matter1
Classification of Matter
  • Compounds may be broken down into their elements through chemical reactions.
  • Elements can not be decomposed into simpler substances via chemical reactions.
  • Compounds can not be broken down into simpler substances via physical processes like boiling or filtering.
classification of matter2
Classification of Matter
  • Much of the matter we encounter is a mixture.
  • A mixture contains two or more pure substances that are physically mixed together.
  • Physical processes can be used to separate mixtures.
    • ex) iron fillings and sand can be separated by using a magnet.
    • ex) sugar and water can be separated by evaporating off all of the water.
classification of matter3
Classification of Matter
  • Mixtures can be classified as either homogeneous or heterogeneous.
    • Homogeneous – means that it is uniform throughout. Air, salt water, and brass are examples of homogeneous mixtures.
    • Heterogeneous – means that it is NOT uniform throughout. A rock, a chocolate chip cookie, and a can of soda are examples of heterogeneous mixtures.
learning check
Learning Check

Identify each of the following as a pure substance or a mixture.

A. pasta and tomato sauce

B. aluminum foil

C. helium

D. air

learning check1
Learning Check

Identify each of the following as a homogeneous or

heterogeneous mixture:

A. hot fudge sundae

B. shampoo

C. sugar water

D. peach pie

elements and symbols
Elements and Symbols
  • All matter consists of primary substances called elements.
  • There are many different types of elements.
  • About 112 different elements are known.
  • Only 88 occur naturally with the rest produced artificially through nuclear reactions (Ch. 9).
elements symbols
Elements & Symbols
  • Elements cannot be decomposed into simpler substances.
  • Elements are the building blocks of all substances.
  • The elements are typically denoted with either a one or two letter designation usually related to the English name or the older Latin name.
elements symbols1
Elements & Symbols
  • The abbreviations for each element are often called its chemical symbol.
  • One letter symbols are always capitalized.
    • C = carbon, N = nitrogen
  • Two letter symbols always have the first letter capitalized with the second one being lowercase.
    • Co = cobalt (CO is the compound carbon monoxide!)
    • Cl = chlorine
latin based symbols
Latin based symbols
  • Some elements have symbols based on their Latin names because they were known to the ancient Greeks.
    • Na (sodium) from natrium
    • Pb (lead) from plumbum
    • Fe (iron) from ferrum
    • K (potassium) from kalium
physical properties
Physical Properties
  • Characteristics of a substance that can be observed or measured without affecting the identity of that substance.
  • Examples include:
    • Color, odor, taste, appearance, density, melting point, and many more.
physical properties of elements
Physical Properties of Elements

Some physical properties of

Copper are:

Color Red-orange

Luster Very shiny

Melting point 1083°C

Boiling point 2567°C

Conduction of electricity Excellent

Conduction of heat Excellent

the periodic table
The Periodic Table
  • Dmitri Mendeleev was the first to arrange the elements in a fashion that showed repeating patterns.
  • This arrangement is called the periodic chart that we use today.
  • You will receive a periodic chart and mark down the groups, periods, metal, non-metal, metalloid designations as well as main and transition areas on your chart.
the elements
The Elements
  • Properties of the Metals
    • metals are found to the left and below the line that separates the elements.
    • metals are shiny solids (except Hg)
    • metals are ductile and malleable (shaped into wires or thin sheets)
    • metals are excellent conductors of both heat and electricity.
the elements1
The Elements
  • Properties of the Non-metals
    • non-metals are found to the right and above the line the separates the elements.
    • non-metals are not shiny, rather those that are solids are dull in color.
    • non-metals are poor conductors.
    • many non-metals are gases at room temperature.
the elements2
The Elements
  • Properties of the Metalloids
    • metalloids are the elements that occur along the line that separate the elements.
    • have properties that are in between that of metals and non-metals.
    • metalloids are semi-conductors.
    • table 3.6 (p. 83) compares a metal, non-metal, and a metalloid.
learning check2
Learning Check

Identify the element described by the following.

A. Group 7A, Period 4

1) Br 2) Cl 3) Mn

B. Group 2A, Period 3

1) beryllium 2) boron 3) magnesium

C. Group 5A, Period 2

1) phosphorus 2) arsenic 3) nitrogen

learning check3
Learning Check

Match the elements to the description.

A. Metals in Group 4A

1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn

B. Nonmetals in Group 5A

1) As, Sb, Bi 2) N, P 3) N, P, As, Sb

C. Metalloids in Group 4A

1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb

the atom
The Atom
  • An atom is the smallest particle of an element that retains the characteristics of that element.
  • Atoms are extremely small – they cannot be seen.
  • John Dalton, theorized the existence of atoms in 1808.
dalton s atomic theory
Dalton’s Atomic Theory
  • All matter is made up of tiny particles called atoms.
  • All atoms of a given element are similar to one another; atoms of different elements are different from each other.
  • Atoms of two or more different elements combine to form compounds.
  • A chemical reaction involves the rearrangement of atoms into new combinations. Atoms are never created nor destroyed in a chemical reaction.
parts of an atom
Parts of an Atom
  • Experiments performed around the turn of the previous century (~1900), showed that atoms were made of several types of particles – collectively referred to as subatomic particles.
  • These experiments showed that three types of particles were present in an atom.
the three particles
The Three Particles
  • A proton has a +1 charge and an approximate mass of 1 amu.
  • Note: an atomic mass unit (amu) is equal to 1/12 of the mass of a Carbon atom with 6 protons and 6 neutrons.
  • A neutron has no charge, but does have a mass of about 1 amu.
  • An electron has a –1 charge and a mass so small that we usually say that it weighs 0 amu.
structure of the atom
Structure of the Atom
  • Ernest Rutherford performed an experiment called the “Gold Foil” experiment in 1911.
  • He used an alpha particle (2P + 2N) source and fired them at a piece of very thin gold foil.
  • He expected all of the particles to pass straight through. However, some were deflected and some were even reflected backwards.
  • In Rutherford’s words, it was as if he had shot a cannonball at a piece of tissue paper and have it bounce backwards.
nuclear model of the atom
Nuclear Model of the Atom
  • Only 1 in 8000 alpha particles is scattered.
  • Scattering occurs when an alpha particle encounters a gold nuclei.
  • A nucleus is very small and contains both the protons and the neutrons. Thus, it contains almost all of the mass of an atom.
  • This very dense center is surrounded by the electron cloud, which is occupied by the fast moving electrons.
  • Thus, an atom is MAINLY EMPTY SPACE.
atomic number mass number
Atomic Number & Mass Number
  • All atoms of the same element have the same number of protons.
  • This distinguishes one element from another.
  • The number of protons is also called the atomic number.
  • This is always the integer found on the periodic chart with each chemical symbol.
atomic number mass number1
Atomic Number & Mass Number
  • Atoms are electrically neutral. Thus, each element must have an equal number of protons and electrons.
  • The mass number of an atom is equal to the sum total of the protons and neutrons in the nucleus.
  • Mass number and atomic weight (found on the periodic chart) are NOT the same thing.
isotopes and atomic mass
Isotopes and Atomic Mass
  • All atoms of one element have the same number of protons.
  • But, they can have different numbers of neutrons, and hence, a different mass number.
  • These different versions of atoms from one element are called isotopes.
isotopic symbols
Isotopic Symbols
  • Use the chemical symbol, atomic number (Z), and mass number (A) as seen below.
  • Can also list symbol followed by mass number.
atomic mass
Atomic Mass
  • The masses found for each element on the periodic chart are the weighted average of all the known isotopes for that element.

Example: Chlorine has only two known isotopes – Cl-35 and Cl-37. Cl-35 is found 75.5% of the time and Cl-37 is found 24.5% of the time.

slide41
Isotope Mass X Percent = Contribution

(approximate) to total mass

35 amu X 0.755 = 26.4 amu

37 amu X 0.245 = 9.1 amu

Totals 1.000 35.5 amu

  • With all elements, round A.W.’s to one decimal place.
study check1
Study Check
  • What is the Atomic Weight of each element rounded to 0.1amu?
    • Na
    • Si
    • Cl
    • K
electron arrangement
Electron Arrangement
  • The electrons determine much of the properties and reactions for that element.
  • Electrons are arranged first into shells, and then further into subshells.
  • Shells are usually indicated by the letter n and have integer values.
  • n = 1 is the lowest energy possible.
shells
Shells
  • The maximum number of electrons that each shell can hold depends on the value of n.
    • n = 1, can hold two electrons maximum.
    • n = 2, can hold eight electrons maximum.
    • n = 3, can hold 18 electrons maximum.
    • n = 4, can hold 32 electrons maximum.
orbitals
Orbitals
  • An orbital is a 3D shape that contains up to two electrons MOST of the time.
  • An s type orbital is spherical in shape.
  • A p type orbital has two lobes along one of the three axes (x, y, or z).
subshells
Subshells
  • Shells are split up into subshells.
  • Each type of subshell is given a letter designation – s, p, d, or f. The s and p orbitals were shown on the previous slide.
  • Each subshell also has a maximum number of electrons that it can hold.
  • s = 2, p = 6, d = 10, and f = 14.
using subshell notation
Using Subshell Notation
  • The filling order for subshells is:
    • 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p,…
  • For writing electron configurations, write each subshell followed by a superscript number indicating the number of electrons.
  • Remember that subshells can only hold as many electrons as stated previously.
what are the electron configurations for
What are the Electron Configurations for:
  • H
  • B
  • O
  • Ne
  • Mg
  • There is a pattern to this!
shorthand method
Shorthand Method
  • For elements with a lot of electrons, the process is rather tedious.
  • The shorthand method uses the noble gases (group 8A) to represent the filled shell(s) of electrons.
  • For any element, count back to the last noble gas encountered. Then, begin with the next subshell until you are finished.
study check2
Study Check
  • Write the shorthand electron configuration for each of the following:
    • Mg
    • S
    • Ti
    • Zn
energy level changes
Energy Level Changes
  • Electrons normally reside in the lowest possible energy levels (called the ground state).
  • In the presence of heat or light, electrons can absorb energy and jump to a higher level (shell #).
  • In time, electrons will return to the lower energy state by emitting energy.
  • Some of these transitions are in turn responsible for the colors we perceive for different objects.
periodic trends
Periodic Trends
  • Many physical and chemical properties can be predicted using the periodic table.
  • Valence electrons are the outermost shell of electrons.
  • For main group elements, the number of valence electrons equals the group number.
    • ex) group 2A elements all have two valence electrons.
    • ex) group 5A elements all have five valence electrons.
periodic trends1
Periodic Trends
  • Electron dot symbols combine the element symbol with the number of valence electrons.
  • Valence electrons are shown as dots, which are placed one on each side (N-S-E-W) until the fifth electron. With the fifth electron, you will begin pairing them up.
  • Table 3.16 shows the Electron dot symbols of the first four periods of the main group elements.
learning check4
Learning Check

A. X is the electron-dot symbol for

1) Na 2) K 3) Al

 

B.  X 

 is the electron-dot symbol of

1) B 2) N 3) P

periodic trends2
Periodic Trends
  • Atomic sizes vary following a pattern.
    • Sizes increase from top to bottom
    • Sizes decrease from left to right
    • Figure 3.15 on p. 100 shows relative sizes
periodic trends4
Periodic Trends
  • Ionization energy is defined as the amount of energy required to remove an electron from an element in its gaseous state.
      • Na(g) + energy  Na+(g) + 1 e-
    • Ionization energy decreases from top to bottom
    • Ionization energy generally increases from left to right (there are exceptions, but don’t worry about these).
learning check5
Learning Check
  • Select the element in each pair with the larger atomic radius.

A. Li or K

B. K or Br

C. P or Cl

learning check6
Learning Check
  • Select the element in each pair with the higher ionization energy.

A. Li or K

B. K or Br

C. P or Cl