Chapter 3
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Transcript of 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 Pure Substance = matter that has a
fixed or definite composition. Both elements and compounds are
examples of pure substances.
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 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 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.
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 Check
Identify each of the following as a homogeneous orheterogeneous mixture:
A. hot fudge sundae
B. shampoo
C. sugar water
D. peach pie
Learning Check
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 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 & 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 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
Elements Essential to LifeElement Where FoundOxygen Water, carbohydrates, fats, proteinsCarbon Carbohydrates, fats, proteinsHydrogen Water, carbohydrates, proteinsNitrogen Proteins, DNA, RNACalcium Bones, teethPhosphorus Bones, teeth, DNA, RNAPotassium Inside cells (nerve impulses)Sulfur Some amino acidsSodium Body fluids (electrolyte)
Elements Essential to LifeElement Where FoundMagnesium Inside cellsChlorine Outside cells (electrolyte)Iron Hemoglobin (blood)Copper EnzymesZinc Metabolism, enzymes, energy production Manganese EnzymesIodine Thyroid regulationFluorine TeethCobalt EnzymesSelenium Antioxidant, ???
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
Some physical properties ofCopper are:
Color Red-orangeLuster Very shinyMelting point 1083°CBoiling point 2567°CConduction of electricity ExcellentConduction of heat Excellent
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 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 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 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.
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 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
Learning Check
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 Theory1. All matter is made up of tiny particles called
atoms.2. All atoms of a given element are similar to one
another; atoms of different elements are different from each other.
3. Atoms of two or more different elements combine to form compounds.
4. 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 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 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 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 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 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 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 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 Use the chemical symbol, atomic
number (Z), and mass number (A) as seen below.
Can also list symbol followed by mass number.
16 - Oor O
A - Xor X16
8
AZ
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.
Isotope Mass X Percent = Contribution
(approximate) to total mass
35 amu X 0.755 = 26.4 amu
37 amu X 0.245 = 9.1 amuTotals 1.000 35.5 amu
With all elements, round A.W.’s to one decimal place.
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 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 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 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 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.
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.
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 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 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.
A. X is the electron-dot symbol for
1) Na 2) K 3) Al B. X
is the electron-dot symbol of1) B 2) N 3) P
Learning Check
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 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 Check Select the element in each pair with the larger
atomic radius.
A. Li or KB. K or BrC. P or Cl