Chapter 19 – Properties of Atoms & the Periodic Table Chapter preview sections 1 Structure of the Atom 2 Masses of Atoms 3 The Periodic Table Atoms Compose All Things, Great and Small Everything in the universe is composed of tiny particles called atoms. You will learn about atoms and their components: protons, neutrons, electrons, and quarks.

Properties of Atoms and the Periodic Table Section 1—Structure of the Atom Original Author: Donna Myers

Scientific Shorthand Elements are abbreviated in scientific shorthand. Consist of one capital letter or a capital letter plus one or two small letters. Some symbols are derived from Latin. Argentum is Latin for “silver”

Learn Table 1 on page 578 Symbols of Some Elements Element Symbol Aluminum Al Gold Au Mercury Hg Calcium Ca Helium He Nitrogen N Carbon C Hydrogen H Oxygen O Chlorine Cl Iodine I Potassium K Copper Cu Iron Fe Silver Ag Fluorine F Magnesium Mg Sodium Na

Atom An element is matter that is composed of one type of atom. Atom is the smallest piece of matter that still has the properties of the element. A chemical symbol represents the name of an element.

Atomic Components Protons—particles with electrical charge of 1+ Neutrons—neutral particles with no electrical charge. Electrons—particles with electrical charge of 1– Nucleus—positively charged central core of the atom

Atomic components Protons and neutrons are in center of nucleus. The region around the nucleus occupied by electrons is called the electron cloud.

Quarks The nucleus of the atom contains protons and neutrons that are composed of particles of matter called quarks. Six quarks are known to exist. Quarks are studied by colliding accelerated charged particles with protons, which leave tracks in a bubble chamber. Bubble chamber image Bubble chamber

Tevatron A tevatron is used to accelerate protons in the study of subatomic particles.

Models Scientists use scale-up models to represent atoms. John Dalton’s atomic model was a simple sphere.

Democritis’s Uncuttable Atom NATIONAL GEOGRAPHIC Visualizing the Atomic Model The ancient Greek philosopher Democritis proposed that elements consist of tiny, solid particles that cannot be subdivided. Democritis’s Uncuttable Atom Thompson Model, 1904 Rutherford Model, 1911 Bohr Model, 1913 See Figure 5, page 582

The Electron Cloud Model (Current) In 1926, scientists developed the electron cloud model of the atom that is used today. This model shows electrons traveling in specific energy levels around a nucleus of protons and neutrons. According to present atomic theory, the location of an electron in an atom cannot be pinpointed exactly.

Masses of Atoms Section 2

Atomic Mass Composed mostly of protons and neutrons. Majority of the mass of an atom is located in the nucleus.

Atomic Mass Units Unit of measurement for atomic particles is atomic mass unit (amu) which is one-twelfth the mass of a carbon atom containing six protons and six neutrons. 1 amu = mass of 1 proton or 1 neutron

Comparison of Particles in an Atom Protons and neutrons are about the same size and mass. Electrons are about 1,836 times smaller than protons and neutrons.

Atomic Number Protons identify the element.

The sum of the number of protons and neutrons in an atom Mass Number The sum of the number of protons and neutrons in an atom Protons + neutrons = mass number A certain atom has 26 protons, 26 electrons, and 30 neutrons. What is its mass number?

Mass Numbers of Some Atoms (page 585) Element Symbol Atomic Number Protons Neutrons Mass Number Average Atomic Mass Boron B 5 6 11 10.81 Carbon C 12 12.01 Oxygen O 8 16 16.00 Sodium Na 23 22.99 Copper Cu 29 34 63 63.55

Isotopes Atoms of the same element with different numbers of neutrons. Different isotopes have different properties. Name of element followed by mass number identifies the isotope. Carbon-12 Carbon-14 Lead-206

Isotopes To find number of neutrons: mass number – atomic number = number of neutrons Atoms of boron have mass numbers of 10 or 11. How many neutrons are in a boron atom? Boron-10 10 – 5 = 5 neutrons Boron-11 11 – 5 = 6 neutrons

Average Atomic Mass The average atomic mass is the weighted-average mass of the mixture of its isotopes. Average atomic mass is closest to its most abundant isotope. Four out of five atoms of boron are boron-11 and one out of five is boron-10 Average atomic mass of boron is close to mass of most abundant isotope, boron-11.

Isotopes The average mass is closest to its most abundant isotope Chlorine’s atomic mass is 35.453. List two possible isotopes of chlorine. Cl-35 and Cl-36

Work Section 2 Assessment, page 587 1) Use paper and pencil (colored if you have them) to draw the electron cloud model for lithium. Include the correct number of protons and electrons. Include four neutrons in the drawing. 2) Calculate the weighted average of the following quiz scores: 5 students scored 80%; 19 students scored 90%. Work Section 2 Assessment, page 587

The Periodic Table Section 3

Periodic Table The modern day periodic table is a chart showing the classifications of elements according to their properties and increasing atomic numbers. The p. t. is useful because it shows the relationship among the elements and it can be used to predict similarities and differences among the elements.

Dmitri Mendeleev Developed the first periodic table He arranged the elements by increasing atomic mass and aligned them in columns based on chemical and physical properties.

Groups On The Periodic Table Elements arranged in vertical columns in the periodic table Elements in a group have similar properties Elements in a group have the same number of electrons in their outer energy level. There are 18 groups

Energy Levels There are 7 energy levels Energy level one contains a maximum of 2 electrons Maximum number of electrons in second energy level is 8. Each row in the periodic table ends when an outer energy level is filled.

Major energy level K L M N O P Q Maximum number of electrons 2 8 18 32

Noble Gases Group 8A on periodic table A complete and very stable electron arrangement in the outer energy level will contain 8 electrons—this very stable arrangement is characteristic of noble gases.

Electron Dot Diagrams Are used to show how electrons in the outer energy level are bonded when elements combine to form compounds.

Periods Horizontal rows of elements that contain increasing numbers of protons and electrons. One proton and one electron are added to each element as you go across the periodic table from left to right.

Classification of Elements All elements in yellow squares are metals. All elements in green squares are nonmetals All elements in purple squares are metalloids or semimetal.

Properties of Metals Most metals exist as solids at room temperature They are shiny, can be drawn into wires, pounded into sheets, and are good conductors of electricity. Moving from left to right in a row of the periodic table, metallic properties of atoms decrease.

Properties of Nonmetals and Metalloids Most are gases Brittle Poor conductors of heat and electricity Metalloids Have some properties of both metals and nonmetals Chlorine gas Boron and silicon

Elements in the Universe All elements throughout the universe are the same. Hydrogen and helium are the building blocks of other naturally occurring elements. Scientist believe that naturally occurring elements are manufactured within stars.