1. Chapter 4 Atomic Structure

2. Democritus Greek Philosopher First to suggest the idea of atoms. Believed atoms were indivisible & indestructible

3. John Dalton English chemist & school teacher. Started the modern idea of the atom.

4. Dalton’s Atomic Theory Dalton’s Atomic Theory: 1. All elements are composed of tiny particles called atoms 2. Atoms of the same element are identical; atoms of one element are different than other elements. 3. Atoms of different elements can physically mix or chemically combine in whole-number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of 1 element are never changed into another element.

5. Dalton’s Atomic Theory

6. Atoms Atom—smallest particle of an element that retains the properties of that element. Atoms can be detected using a scanning tunneling microscope. The Elements: Forged in Stars The Origin of the Elements

7. Sec 2: Nuclear Atom Atoms are now known to be divisible. Atoms are composed of electrons, protons, and neutrons. Electrons—negatively charged subatomic particles. Electrons were discovered by J.J. Thomson using a cathode ray. Negative electrons are attracted to positively charged metal plates.

8. Nucleus Nucleus—the central core of an atom composed of protons & neutrons. The nucleus was discovered by Ernest Rutherford using the gold foil experiment.

9. Protons & Neutrons Protons—positively charged subatomic particles. Neutrons—subatomic particles with no charge. Discovered by Chadwick 1932 Discovered by Chadwick 1932 Mass of neutron is about equal to proton (1 amu) Mass of neutron is about equal to proton (1 amu) Atoms are neutral; they have no overall charge. Positive protons cancel out negative electrons Positive protons cancel out negative electrons

10. Isotopes Isotopes—Atoms that have the same number of protons, but different numbers of neutrons.

11. Atomic Number Atomic Number—the number of protons in an atom of an element. Every element has a different number of protons.

12. Mass Number Mass number—the total number of protons and neutrons in an atom Mass # = protons + neutrons Mass # = protons + neutrons Example: a helium atom has 2 protons and 2 neutrons. What is the mass number? Example: a helium atom has 2 protons and 2 neutrons. What is the mass number? 4 # of neutrons = mass # – atomic # # of neutrons = mass # – atomic # Shorthand notation: You can use the mass number to name specific atoms. Example: Helium-4

13. Sec. 3: Atomic Mass The mass of a proton or neutron is 1.67 x 10 -24 g. The mass of an electron is 9.11 x 10 -28 g. This is negligible in comparison. This is negligible in comparison. Atomic mass unit (amu)—the 1/12 the mass of a Carbon-12 atom. The approx. mass of a proton or neutron. The approx. mass of a proton or neutron.

14. Atomic Mass Atomic mass—a weighted average mass of the atoms in a naturally occurring sample of the element. The atomic mass is usually closest to the most abundant isotope of that element.

15. Atomic Mass To calculate atomic mass, you need to know 1. The mass of each isotope 2. The natural abundance of each isotope. (in decimal form) Atomic mass of each isotope x its abundance then add the results. Example: Element B has 2 isotopes. One isotope has a mass of 10.012 amu with an abundance of 19.92%. The other isotope has a mass of 11.009 amu with an abundance of 80.09%. What is the atomic mass?

16. Calculating Atomic Mass 10.012 amu x 0.1991 = 1.993 amu 11.009 amu x 0.8009 = 8.817 amu atomic mass = 10.810 amu Done with Section 3

17. Sec. 4 The Periodic Table Development of the Periodic Table: About 70 elements were discovered before the 1880s About 70 elements were discovered before the 1880s Dmitri Mendeleev first listed elements in a systematic, organized way. Dmitri Mendeleev first listed elements in a systematic, organized way. He arranged atoms by their properties and in order of atomic mass. He arranged atoms by their properties and in order of atomic mass. Mendeleev constructed the first periodic table. Mendeleev constructed the first periodic table. He left blank places for unknown elements. He left blank places for unknown elements. Henry Moseley determined atomic # and arranged elements by this instead of atomic mass. Henry Moseley determined atomic # and arranged elements by this instead of atomic mass.

18. The Modern Periodic Table Each element is represented by its symbol and atomic number placed in a square The horizontal arrangement of elements are called periods. Periodic Law—when the elements are arranged in order of increasing atomic number, there is a repeated pattern of physical and chemical properties.

19. The Modern Periodic Table Group—a vertical arrangement of atoms. The elements in any group have similar chemical and physical properties. Each group is identified by a number and letter A or B.

20. The Modern Periodic Table Group A elements are known as representative elements. Representative elements are broken into 3 classes. Metals—high electrical conductivity and luster Metals—high electrical conductivity and luster Alkali metals—Group 1A Alkali metals—Group 1A Alkaline Earth Metals—Group 2A elements Alkaline Earth Metals—Group 2A elements Most non-representative elements are also metals

21. The Modern Periodic Table Nonmetals—occupy upper right corner of the periodic table. Nonlustrous and poor conductors of electricity. S Some are gases, some are solids 2 nonmetal groups have special names Halogens—group 7A (ex. chlorine & bromine) Noble gases—group 8A (or group 0) Inert gases—they do not undergo chemical reactions Ex. Neon gas is used in neon lights.

22. The Modern Periodic Table Metalloids—elements with properties that are intermediate between metals and nonmetals. A heavy line divides metals from nonmetals. Most elements that border this line are metalloids.