chapter 4 atoms and elements - lower moreland township

Chapter 4 Atoms & Elements September 11, 2016

Chapter 4 Atoms and ElementsPeriodic Table

Periods and GroupsOn the periodic table,

• groups contain elements with similar properties and are arranged in vertical columns ordered from left to right.

• periods are the horizontal rows of elements, and they are counted from the top as Period 1 to Period 7.

Group NumbersGroup numbers use• numbers to identify the columns from left to right.• the letter A for the representative elements (1A to 8A) and the letter B for the

transition elements.The representative elements include the first 2 groups, 1A (1) and 2A (2), in addition to groups 3A (13), 4A (14), 5A (15), 6A (16),

7A (17), and 8A (18).

Periods and Groups

Learning CheckIdentify the element described by the following:1. Group 7A (17), Period 4 A. Br B. Cl C. Mn2. Group 2A (2), Period 3 A. beryllium B. magnesium C. boron 3. Group 5A (15), Period 2 A. phosphorus B. arsenic C. nitrogen


Alkali MetalsGroup 1A (1), the alkali metals, includes lithium sodium, potassium, rubidium and cesium. The reactivity of these elements increases from the top to bottom of the group.

Halogens Group 7A (17), the

halogens, includes fluorine, chlorine, bromine, iodine, and astatine. Fluorine and chlorine are highly reactive.

Nobel GasesGroup 8A (18) is the nobel gases, which include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Ra).

Nobel gas elements are unreactive and are seldom found in combination with other elements.

Representative Elements


Metals, Nonmetals, and MetalloidsThe heavy zigzag line separates metals and nonmetals.

• Metals (blue) are located to the left.• Nonmetals (yellow) are located to the right. • Metalloids (green) are located along the heavy zigzag line between the metals and

nonmetals

Properties of Metals, Nonmetals, and MetalloidsMetals are • shiny and ductile.• good conductors of heat and electricity.Nonmetals are • not especially shiny, ductile, or malleable.• poor conductors of heat and electricity.Metalloids are• better conductors than nonmetals, but not as good as metals.• used as semiconductors and insulators.

Comparing a Metal, a Metalloid, and a Nonmetal

Major Elements Essential to HealthEssential elements in a 60-kg adult:


Learning CheckA. Identify each of the following elements as a metal, a nonmetal, or a metalloid.1. sodium ____2. chlorine ____3. silicon ____4. iron ____5. carbon ____

B. Match the elements to the description.1. Metals in Group 4A (14)

A. Sn, Pb B. C, Si C. C, Si, Ge, Sn2. Nonmetals in Group 5A (15)

A. As, Sb, Bi B. N, P C. N, P, As, Sb3. Metalloids in Group 4A (14)

A. C, Si, Ge, B. Si, Ge C. Si, Ge, Sn, Pb

Dalton’s Atomic TheoryDalton theorized that Atoms• are tiny particles of matter too

small to see,• are able to combine with other

atoms to make compounds, and• are similar to each other for

each element and different from atoms of other elements.

A chemical reaction is the rearrangement of atoms.

Images of nickel atoms are produced when nickel is magnified millions of times by a scanning tunneling microscope (STM). This instrument generates an image of the atomic structure.

Subatomic ParticlesAtoms contain subatomic particles such as• Protons, which have a positive (+) charge;• electrons, which have a negative (–) charge; and• neutrons, which have no charge.Experiments show that like charges repel and unlikecharges attract.


J.J Thomson (1856 - 1940) - atom is a ball of positive charge containing a number of electrons. Plum Pudding model

Experiment: Cathode Ray Tube

Cathode Ray Tubes were in nearly every home in the old TV and computer monitors.

Atoms – an atom is the smallest unit of matter. Each kind of atom is called an element.

Rutherford’s Gold-Foil ExperimentDiscovery of the nucleus 1908

(a) Positive particles are aimed at a piece of gold foil. (b) Particles that comeclose to the atomic nuclei of gold are deflected from their straight path.


In Rutherford’s gold-foil experiment, positively charged particles were aimed at atoms of gold and most went straight through the atoms, but some were deflected only occasionally.

Conclusion: There must be a small, dense,

positively charged nucleus in the atom that deflects positive particles that come close.

Structure of the Atom

Atomic Mass ScaleOn the atomic mass scale for subatomic particles,1 atomic mass unit (amu)

is defined as 1/12 of the mass of the carbon-12 atom.

Particles in the Atom

An atom consists of• a nucleus that contains

protons and neutrons, and• electrons in a large, empty

space around the nucleus.


Atomic NumberThe atomic number • is specific for each element • is the same for all atoms of an element• is equal to the number of protons in an atom• appears above the symbol of an element in the Periodic Table

Atomic Number

Symbol

Atomic Number = Protons in AtomFor example, atomic number = number of protons:Atomic number H is 1; every H atom has one protonAtomic number of C is 6; every C atom has six protonsAtomic number of Cu is 29; every Cu atom has 29 protons

Atoms Are NeutralFor neutral atoms, the net charge is zero.

number of protons = number of electronsAluminum has 13 protons and 13 electrons. The net (overall) charge is zero.

13 protons (13+) + 13 electrons (13–) = 0

Learning CheckUse the periodic table to fill in the atomic number, number of protons, and

number of electrons for each of the following elements:

Element Atomic Number Protons Electrons

N

Zn

S


Mass NumberThe mass number• represents the number of particles in the nucleus• is equal to the number of protons + the number of neutrons• is always a whole number• does not appear in the periodic table

Study Tips: Protons and NeutronsNumber of protons = atomic numberNumber of protons + neutrons = mass numberNumber of neutrons = mass number – atomic numberNote: Mass number is given for specific isotopes only.

IsotopesIsotopes • are atoms of the same element that have different mass numbers.• have the same number of protons but different numbers of neutrons.• can be distinguished by atomic symbols.

Isotopes and Mass and Atomic SymbolsSince each isotope of an element has a different number of neutrons, each

isotope’s mass number will be different. We write these as atomic symbols:• Mass numbers are in the upper left corner.• Atomic numbers are in the lower left corner.Example: An atom of sodium with atomic number 11 and a mass number 23

has the following atomic symbol:mass number

atomic number23

Na11


Atomic SymbolsFor an atom, the atomic symbol gives the number of • protons (p+),• neutrons (n), and• electrons (e–).

Learning Check Naturally occurring carbon consists of three isotopes: C-12, C-13, and

C-14. State the number of protons,neutrons, and electrons in each of the following.

Learning Check1. Write the nuclear symbols for atoms with the following subatomic particles:

1. 9 p+, 10 n, 9 e–

2. 17p+, 20 n, 17 e–

3. 47p+, 60 n, 47 e–

2. Which of the following pairs are isotopes of the same element?3. In which of the following pairs do both atoms have 8 neutrons?


Isotopes of SulfurA sample of naturally occurring sulfur containsseveral isotopes with the following abundances:

Atomic MassThe atomic mass of an element• is listed below the symbol of each element on the

periodic table.• gives the mass of an “average” atom of each element

compared to C-12.• is not the same as the mass number.• is calculated using a weighted average.

Most elements have two or more isotopes that contribute to the atomic mass of that element.

Atomic Mass for ClThe atomic mass of chlorine is• based on all naturally occurring Cl isotopes.• not a whole number.• the weighted average of the Cl-35 and Cl-37 isotopes.

The atomic mass of Mg is• based on all naturally occurring Mg isotopes.• not a whole number.

• the weighted average and its mass. of the Mg-24, Mg-25, and Mg-26 isotopes.

Atomic Mass for Mg

chapter 4 atoms and elements - lower moreland township

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