Chapter 16 – Properties of atoms and the Periodic Table Table of Contents Chapter 16 – Properties of atoms and the Periodic Table 17.1: Structure of the Atom 17.2: Masses of Atoms 17.3: The Periodic Table

Structure of the Atom Scientific Shorthand

Scientific shorthand - Element symbols Element symbols must have only one capital letter May have one or two letters Ex: Temporary symbols have three letters and are named for their number.

Elements named for: People: Places: Latin:

Structure of the Atom Atomic Components Atom-smallest piece of matter that still retains the property of the element. Can’t be broken down and still be that element. Atoms are composed of subatomic particles called protons, neutrons, and electrons.

A carbon atom A carbon atom has 6 of each subatomic particle. It has: 6 protons (atomic number is 6 on periodic table) in the nucleus 6 electrons outside nucleus 6 neutrons in nucleus

Structure of the Atom 17.1 Atomic Components Nucleus- positively charged center of the atom that contains protons (positive) and neutrons (neutral). Surrounded by electrons (negative) in a cloud. Protons- particles with an electrical charge of 1+.

Structure of the Atom 17.1 Atomic Components Electrons- particles with an electrical charge of 1–. Found outside nucleus; always moving. Neutrons are neutral particles that do not have an electrical charge. Found in the nucleus

Quarks—Even Smaller Particles Structure of the Atom Quarks—Even Smaller Particles Quarks are even smaller particles that make up protons and neutrons. So far, scientists have confirmed the existence of six uniquely different quarks.

Quarks—Even Smaller Particles Structure of the Atom Quarks—Even Smaller Particles Scientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton. Another arrangement of three quarks produces a neutron It took a team of 450 scientists to identify the sixth quark! A “tevatron” is an instrument that allows to investigate quarks; in Illinois. The Large Hadron Collider is in Switzerland also studies these particles

The Changing Atomic Model Structure of the Atom The Changing Atomic Model Models help us understand what we can’t see. Examples: a globe, planets around the sun, the atom Atomic models have changed over the years.

Democritus’ model, 400BC; an atom is a simple sphere that couldn’t be broken up.

Thomson Model, 1904 an atom is a ball of positive charge with negative charged electrons embedded

Rutherford’s model, 1911 An atom has positive nucleus with electrons surrounding

Bohr model; 1913 An atom has electrons in fixed orbits surrounding nucleus. Electrons can jump orbits if absorbing energy.

John Dalton’s atomic theory (1800’s) is still mostly valid today Six parts of Dalton’s theory: Matter is made of atoms Atoms are indivisible and indestructible Atoms of one element are identical Atoms of one element are different than atoms of another Different atoms combine in whole number ratios to make compounds In chemical reactions, atoms are rearranged.

Current model: the electron cloud model Current model: the electron cloud model. Atom is mostly empty space with electrons. Nucleus is very tiny with most all of the mass there.

The Electron Cloud Model Structure of the Atom The Electron Cloud Model electron cloud- area around the nucleus of an atom where electrons are found.

The Electron Cloud Model Structure of the Atom The Electron Cloud Model The electron cloud is 100,000 times larger than the diameter of the nucleus. In contrast, each electron in the cloud is much smaller than a single proton. Because an electron's mass is small and the electron is moving so quickly around the nucleus, it is impossible to describe its exact location in an atom.

Section Check Question 1 Which is the smallest piece of matter that still retains the property of the element? A. atom B. quark C. neutron D. proton

Section Check Answer The answer is A. An atom is the smallest piece of matter that still retains the property of the element.

Question 2 What particles are found in the nucleus of an atom? Section Check Question 2 What particles are found in the nucleus of an atom? A. protons and electrons B. protons and neutrons C. neutrons and electrons D. quarks and electrons

Section Check Answer The answer is B. Electrons are located in an electron cloud surrounding the nucleus of the atom.

Section Check Question 3 What is the name of the small particles that make up protons and neutrons? Answer Protons and neutrons are made of smaller particles called quarks.

Masses of Atoms Atomic Mass

Masses of Atoms Atomic Mass The mass of a proton is about the same as that of a neutron

Masses of Atoms Atomic Mass The mass of each a proton and a neutron is approximately 1,836 times greater than the mass of the electron.

Masses of Atoms Atomic Mass atomic mass unit (amu)- unit of measurement used for atomic particles – you can’t measure one in lab; it’s way too small Defined as exactly 1/12 of the mass of a carbon atom proton and neutron each weigh 1 amu. All the mass is in the nucleus Electrons weigh 0 amu

Atomic mass The atomic mass is the DECIMAL NUMBER on the periodic table. It represents an average mass of all the types of atoms of that element The atomic mass of carbon is ___________ The atomic mass of zinc is ____________ The atomic mass of barium is ___________

Protons Identify the Element Masses of Atoms Protons Identify the Element atomic number- The number of protons in an atom The number of protons tells you what type of atom you have For example, every carbon atom has six protons. Also, all atoms with six protons are carbon atoms.

Atomic number The atomic number is the WHOLE NUMBER found on the periodic table The atomic number tells how many PROTONS there are Ex: phosphorus has atomic number ____ and has _________ protons Ex: chlorine has atomic number ________ and that means it has ________ _______

Masses of Atoms Mass Number mass number- defined as the sum of the number of protons and the number of neutrons in the atom. It is a WHOLE NUMBER (no decimals) It is often very close to the atomic mass, but it is NOT THE SAME as atomic mass

Masses of Atoms Mass Number If you know the mass number and the atomic number of an atom, you can calculate the number of neutrons. FORMULA: number of neutrons = mass number – atomic number

Masses of Atoms Isotopes Not all the atoms of an element have the same number of neutrons. isotopes Atoms of the same element that have different numbers of neutrons Ex: C-12 has ____ protons and ____ neutrons Ex: C-14 has ____ protons and ______ neutrons Ex: U-238 has ____ protons and ____ neutrons Ex U- 235 has ____ protons and ____ neutrons

Masses of Atoms Identifying Isotopes Models of two isotopes of boron are shown. Because the numbers of neutrons in the isotopes are different, the mass numbers are also different. You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11.

Masses of Atoms Identifying Isotopes average atomic mass- is the weighted-average mass of the mixture of its isotopes. It should equal the decimal number on the periodic table For example, four out of five atoms of boron are boron-11, and one out of five is boron-10. To find the weighted-average or the average atomic mass of boron, you would solve the following equation:

Question 1 Answer How is the atomic number of an element determined? Section Check Question 1 How is the atomic number of an element determined? Answer The atomic number of an element is equal to the number of protons in an atom of that element.

Section Check Question 2 The element helium has a mass number of 4 and atomic number of 2. How many neutrons are in the nucleus of a helium atom?

Section Check Answer Recall that the atomic number is equal to the number of protons in the nucleus. Since the mass number is 4 and the atomic number is 2, there must be 2 neutrons in the nucleus of a helium atom.

Section Check Question 3 How much of the mass of an atom is contained in an electron? Answer The electron’s mass is so small that it is considered negligible when finding the mass of an atom.

Organizing the Elements The Periodic Table Organizing the Elements Periodic means "repeated in a pattern." In the late 1800s, Dmitri Mendeleev, a Russian chemist, searched for a way to organize the elements. When he arranged all the elements known at that time in order of increasing atomic masses, he discovered a pattern.

Organizing the Elements The Periodic Table Organizing the Elements Because the pattern repeated, it was considered to be periodic. Today, this arrangement is called a periodic table of elements. In the periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties.

Mendeleev's Predictions The Periodic Table Mendeleev's Predictions Mendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties. He looked at the properties and atomic masses of the elements surrounding these blank spaces.

Mendeleev's Predictions The Periodic Table Mendeleev's Predictions From this information, he was able to predict the properties and the mass numbers of new elements that had not yet been discovered.

Mendeleev's Predictions The Periodic Table Mendeleev's Predictions This table shows Mendeleev's predicted properties for germanium, which he called ekasilicon. His predictions proved to be accurate.

Improving the Periodic Table On Mendeleev's table, the atomic mass gradually increased from left to right. If you look at the modern periodic table, you will see several examples, such as cobalt and nickel, where the mass decreases from left to right.

Improving the Periodic Table In 1913, the work of Henry G.J. Moseley, a young English scientist, led to the arrangement of elements based on their increasing atomic numbers instead of an arrangement based on atomic masses. The current periodic table uses Moseley's arrangement of the elements.

The Atom and the Periodic Table The vertical columns in the periodic table are called groups, or families, and are numbered 1 through 18. Horizontal rows are called series or periods. There are seven of these Elements in each group have similar properties.

Electron Cloud Structure The Periodic Table Electron Cloud Structure In a neutral atom, the number of electrons is equal to the number of protons. Therefore, a carbon atom, with an atomic number of __________ has ___________protons and __________ electrons.

Electron Cloud Structure The Periodic Table Electron Cloud Structure Scientists have found that electrons within the electron cloud have different amounts of energy. 1st energy level holds a max of 2 electrons 2nd energy level holds a max of 8 electrons 3rd energy levels holds a max 18 electrons 4th energy level holds a max of 32 electrons There is much overlap in filling electrons

Electron Cloud Structure The Periodic Table Electron Cloud Structure Scientists model the energy differences of the electrons by placing the electrons in energy levels.

Electron Cloud Structure The Periodic Table Electron Cloud Structure Energy levels nearer the nucleus have lower energy than those levels that are farther away. Electrons fill these energy levels from the inner levels (closer to the nucleus) to the outer levels (farther from the nucleus).

Electron cloud structure for nitrogen-14

Sulfur-32 16 protons, 16 neutrons, 16 electrons

What element?

The Periodic Table Energy Levels A complete and stable outer energy level will contain eight electrons. This is called the octet rule

Electron Cloud Structure The Periodic Table Electron Cloud Structure Elements that are in the same group have the same number of electrons in their outer energy level – these are valence electrons. The most valence electrons is eight. Elements in group 1 have 1 valence electron Elements in group 2 have 2 valence electrons Elements in group 13 have 3 valence electrons Elements in group 14 have 4 valence electrons Group 15 – has 5 valence electrons Group 16 – has 6 valence electrons Group 17 – has 7 valence Group 18 – has 8 valence

It is the number of valence electrons in the outer energy level that determines the chemical properties of the element. For example: arsenic has 33 total electrons, but only 5 valence electrons. These 5 are what react. Barium has _______ total electrons, but only ______ valence electrons.

The Periodic Table Rows on the Table Remember that the atomic number found on the periodic table is equal to the number of total electrons in an atom.

The Periodic Table Rows on the Table The first row has hydrogen with one electron and helium with two electrons both in energy level one. Energy level one can hold only two electrons. Therefore, helium has a full or complete outer energy level.

The Periodic Table Rows on the Table The second row begins with lithium, which has three total electrons—two in energy level one and one in energy level two. There is one valence electron. Lithium is followed by beryllium with two outer electrons, boron with three, and so on until you reach neon with eight outer electrons.

The Periodic Table Rows on the Table Do you notice how the row in the periodic table ends when an outer level is filled? In the third row of elements, the electrons begin filling energy level three. The row ends with argon, which has a full outer energy level of eight electrons [eight valence electrons – follows the octet rule.

Columns - Electron Dot Diagrams The Periodic Table Columns - Electron Dot Diagrams Elements that are in the same group (family, or column) have the same number of valence electrons in their outer energy level. These outer electrons are so important in determining the chemical properties of an element that a special way to represent them has been developed.

The Periodic Table Electron Dot Diagrams An electron dot diagram uses the symbol of the element and dots to represent the electrons in the outer energy level. Electron dot diagrams are used also to show how the valence electrons in the outer energy level are bonded when elements combine to form compounds.

Same Group—Similar Properties The Periodic Table Same Group—Similar Properties The elements in Group 17, the halogens, have electron dot diagrams similar to chlorine. All halogens have seven valence electrons.

Same Group—Similar Properties The Periodic Table Same Group—Similar Properties A common property of the halogens is the ability to form compounds readily with elements in Group 1. The Group 1 element, sodium, reacts easily with the Group 17 element, chlorine. The result is the compound sodium chloride, or NaCl—ordinary table salt.

Same Group—Similar Properties The Periodic Table Same Group—Similar Properties Not all elements will combine readily with other elements. The elements in Group 18 have complete outer energy levels. This special configuration makes Group 18 elements relatively unreactive.

Regions on the Periodic Table The periodic table has several regions with specific names. The horizontal rows of elements on the periodic table are called periods. The elements increase by one proton and one electron as you go from left to right in a period.

Regions on the Periodic Table All of the elements in the blue squares are metals.

Regions on the Periodic Table Those elements on the right side of the periodic table, in yellow, are classified as nonmetals.

Regions on the Periodic Table The elements in green are metalloids or semimetals.

The Periodic Table A Growing Family In 1994, scientists at the Heavy-Ion Research Laboratory in Darmstadt, Germany, discovered element 111. Element 112 was discovered at the same laboratory. Both of these elements are produced in the laboratory by joining smaller atoms into a single atom.

Elements in the Universe The Periodic Table Elements in the Universe Using the technology that is available today, scientists are finding the same elements throughout the universe. Many scientists believe that hydrogen and helium are the building blocks of other elements.

Elements in the Universe The Periodic Table Elements in the Universe Exploding stars, or supernovas, give scientists evidence to support this theory. Many scientists believe that supernovas have spread the elements that are found throughout the universe.

Question 1 17.3 How are the elements arranged in the periodic table? Section Check 17.3 Question 1 How are the elements arranged in the periodic table?

Section Check 17.3 Answer The elements are arranged by increasing atomic number and by changes in physical and chemical properties.

Section Check 17.3 Question 2 What do the elements in a vertical column of the periodic table have in common?

Section Check 17.3 Answer The vertical columns in the periodic table are called groups; elements in the same group have similar properties, such as electrical conductivity.

Section Check 17.3 Question 3 What do the dots in this electron dot diagram represent?

Section Check 17.3 Answer The dots represent the electrons in the outer energy level.

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