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.

Elements are composed of only one type of atom.

Compounds are composed of two or more elements, but always in the same ratio.

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 Found

Oxygen Water, carbohydrates, fats, proteins

Carbon Carbohydrates, fats, proteins

Hydrogen Water, carbohydrates, proteins

Nitrogen Proteins, DNA, RNA

Calcium Bones, teeth

Phosphorus Bones, teeth, DNA, RNA

Potassium Inside cells (nerve impulses)

Sulfur Some amino acids

Sodium Body fluids (electrolyte)

Elements Essential to LifeElement Where Found

Magnesium Inside cells

Chlorine Outside cells (electrolyte)

Iron Hemoglobin (blood)

Copper Enzymes

Zinc Metabolism, enzymes, energy production

Manganese Enzymes

Iodine Thyroid regulation

Fluorine Teeth

Cobalt Enzymes

Selenium 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.

Groups with Special Names

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.

Nuclear Model of the Atom

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.

Study Check

Name Symbol Atomic # Mass # #P #N #e

Carbon 12

N 8

26 30

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.

Study Check What is the Atomic Weight of each

element rounded to 0.1amu? Na Si Cl K

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).

Orbitals

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.

What are the Electron Configurations for: H B O Ne Mg There is a pattern to this!

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 Check Write the shorthand electron

configuration for each of the following: Mg S Ti Zn

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 of

1) 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

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).

Periodic Trends

Learning Check

Select the element in each pair with the larger atomic radius.

A. Li or KB. K or BrC. P or Cl

Learning Check

Select the element in each pair with the higher ionization energy.

A. Li or KB. K or BrC. P or Cl