Atoms and the Periodic Table Mr. Holmes

Russian chemist, Dimitri Mendeleev, searched for a way to organize the elements in the 1800’s. Russian chemist, Dimitri Mendeleev, searched for a way to organize the elements in the 1800’s. He arranged the elements in order of increasing mass, which revealed a pattern in their chemical properties. He arranged the elements in order of increasing mass, which revealed a pattern in their chemical properties. Elements are arranged by increasing atomic number and chemical properties. Elements are arranged by increasing atomic number and chemical properties.

In 1800, there were only 31 elements to organize. In 1800, there were only 31 elements to organize. Elements can appear in three various states: Elements can appear in three various states: –Solids –Liquids (aqueous) –Gases (gaseous)

The periodic table is divided into three different regions (families) The periodic table is divided into three different regions (families) –Metal –Nonmetals –Metalloids There are two groups within the nonmetals There are two groups within the nonmetals –Noble gases –Halogens (are a series of nonmetal elements from Group 17)

The horizontal rows of the periodic table are called periods. The horizontal rows of the periodic table are called periods. Elements increase by one proton and one electron as you go from left to right on the periodic table. Elements increase by one proton and one electron as you go from left to right on the periodic table. Each vertical column in the periodic table is a group, which make up the families. Each vertical column in the periodic table is a group, which make up the families. Each group is given a roman numeral. Each group is given a roman numeral.

Aristotle Early Greek Theories 400 B.C. - Democritus thought matter could not be divided indefinitely. 400 B.C. - Democritus thought matter could not be divided indefinitely. 350 B.C - Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. Democritus Aristotle was wrong. However, his theory persisted for 2000 years. fire air water earth This led to the idea of atoms in a void.

John Dalton Dalton proposed a modern atomic model Dalton proposed a modern atomic model based on experimentation not on pure reason. All matter is made of atoms. Atoms of an element are identical. Each element has different atoms. Atoms of different elements combine in constant ratios to form compounds. Atoms are rearranged in reactions. His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).

Adding Electrons to the Model 1) Dalton’s “Billiard ball” model ( ) Atoms are solid and indivisible. 2)Thompson “Plum pudding” model (1900) Negative electrons in a positive framework. 3)The Rutherford model (around 1910) Atoms are mostly empty space. Negative electrons orbit a positive nucleus. Materials, when rubbed, can develop a charge difference. This electricity is called “cathode rays” when passed through an evacuated tube (demos). These rays have a small mass and are negative. Thompson noted that these negative subatomic particles were a fundamental part of all atoms.

Ernest Rutherford (movie: 10 min.) Most particles passed through. So, atoms are mostly empty. Some positive  -particles deflected or bounced back! Thus, a “nucleus” is positive & holds most of an atom’s mass. Radioactive substance path of invisible  -particles Rutherford shot alpha (  ) particles at gold foil. Rutherford shot alpha (  ) particles at gold foil. Lead block Zinc sulfide screenThin gold foil

Atoms are the basic unit of matter. Atoms are the basic unit of matter. Atoms are made of small subatomic particles: Atoms are made of small subatomic particles: –Protons –Neutrons –Electrons Protons and neutrons are made up of 3 smaller particles called quarks. Protons and neutrons are made up of 3 smaller particles called quarks.

Electrons have a negative charge Electrons have a negative charge Protons have a positive charge Protons have a positive charge Neutrons have no charge Neutrons have no charge Protons and neutrons make up the nucleus Protons and neutrons make up the nucleus Electrons surround the nucleus Electrons surround the nucleus

The Atom Protons and neutrons are the same size and mass. Protons and neutrons are the same size and mass. Electrons are much smaller and lighter than protons and neutrons Electrons are much smaller and lighter than protons and neutrons

Atomic numbers, Mass numbers There are 3 types of subatomic particles. We already know about electrons (e – ) & protons (p + ). Neutrons (n 0 ) were also shown to exist (1930s). There are 3 types of subatomic particles. We already know about electrons (e – ) & protons (p + ). Neutrons (n 0 ) were also shown to exist (1930s). They have: no charge, a mass similar to protons They have: no charge, a mass similar to protons Elements are often symbolized with their mass number and atomic number Elements are often symbolized with their mass number and atomic number E.g. Oxygen: O 16 8 These values are given on the periodic table. These values are given on the periodic table. For now, round the mass # to a whole number. For now, round the mass # to a whole number. These numbers tell you a lot about atoms. These numbers tell you a lot about atoms. # of protons = # of electrons = atomic number # of protons = # of electrons = atomic number # of neutrons = mass number – atomic number # of neutrons = mass number – atomic number Calculate # of e –, n 0, p + for Ca, Ar, and Br. Calculate # of e –, n 0, p + for Ca, Ar, and Br.

Br Ar Ca e–e–e–e– n0n0n0n0 p+p+p+p+MassAtomic

3 p + 4 n 0 2e – 1e – Li shorthand Bohr - Rutherford diagrams Putting all this together, we get B-R diagrams Putting all this together, we get B-R diagrams To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order) To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order) Draw protons (p + ), (n 0 ) in circle (i.e. “nucleus”) Draw protons (p + ), (n 0 ) in circle (i.e. “nucleus”) Draw electrons around in shells Draw electrons around in shells 2 p + 2 n 0 He 3 p + 4 n 0 Li Draw Be, B, Al and shorthand diagrams for O, Na

11 p+ 12 n° 2e – 8e – 1e – Na 8 p+ 8 n° 2e – 6e – O 4 p+ 5 n° Be 5 p+ 6 n° B 13 p+ 14 n° Al

The groups of the periodic table also tell you the number of valence electrons of each atom. The groups of the periodic table also tell you the number of valence electrons of each atom. The periods tell the valence shell of the element. The periods tell the valence shell of the element.

1A 2A 3A4A5A6A7A 8A

Isotopes have the same number of protons but differ in their number of neutrons. Isotopes have the same number of protons but differ in their number of neutrons. Boron, for example, naturally appears as B-11. An isotope of B-11 would be B-10 and B-12 Boron, for example, naturally appears as B-11. An isotope of B-11 would be B-10 and B-12

Isotopes Which of the following is an isotope? Which of the following is an isotope? a.Li-8 b.Mg-24 c.N-14 d.C-13

Compounds A substance formed by the chemical combination of two or more elements in definite proportions. A substance formed by the chemical combination of two or more elements in definite proportions. Compounds are formed by forming chemical bonds Compounds are formed by forming chemical bonds Bond formation involves the electrons that surround each atomic nucleus. Bond formation involves the electrons that surround each atomic nucleus.

Types of Chemical Bonds Covalent Bonds Covalent Bonds –Sharing of electrons between molecules Ionic Bonds Ionic Bonds –Transfer of electrons between molecules Van der Waals Forces Van der Waals Forces –Intermolecular forces of attraction between molecules