Atomic Structure and the Periodic Table Atomic Models

Atomic Structure and the Periodic Table Atomic Models Democritus’s Model - He was a teacher in the 4 th Century B. C. - He believed that all matter was composed of small indivisible and indestructible particles - He called these particles atoms

Dalton’s Model: 1. Elements are composed of tiny indivisible particles 2. Atoms of the same element are identical 3. Atoms of different elements can physically mix together or chemically combine in simple whole number ratios 4. Chemical reactions occur when atoms are separated, joined, or rearranged 5. Atoms of one element never change into atoms of another element

J. J. Thompson’s Model: - He was an English Physicist - He passes electric current through gases at low pressure using a cathode ray - Negative particles were repelled by negative plates and the po were attracted to the negative plates - He was the first person to discover electrons

Rutherford’s Model: http: //www. shsu. edu/%7 Echm_tgc/sounds/pushmovies/l 2 ruther. gif - He found that the center of an atom is dense and has a positive charge - Most of the atom is made of empty space and in that empty space there are negative charges (the electrons)

Bohr’s Model: - He found that the nucleus of an atom contains protons and neutrons - He also found that the electrons do not move about randomly outside the nucleus - He believed that the electrons traveled in paths he called Orbits

The Quantum Mechanical Model - The atomic model that is accepted today - Protons and neutrons are still found in the nucleus and the electrons are outside the nucleus but the electrons are not found in orbits. - Electrons occupy a space in which they are free to move in called an orbital

Basic Information About Atoms are the smallest part of an element that retains the properties of that ele We can now see atoms using a scanning tunneling microscope What are atoms made of? Protons - Have a charge of positive one - Have a mass of 1 amu (atomic mass unit) - Are located in the nucleus of an atom Neutrons - Are neutrally charged - Have a mass of 1 amu - Are located in the nucleus

Electrons - Have a charge of negative one - Are located outside of the nucleus in orbitals - The have a mass of 1/1840 amu - Are the only particles that can enter and leave atoms The nucleus takes up a very small part of the space in an atom. - If an atom were the size of a football stadium the nucleus would be the size of a marble

Numbers derived from atoms and put on the periodic table. Atomic Number (Z): the number of protons in an atom - It is this different number of protons that makes each element different Mass Number: the number of protons added to the number of neutrons - The number of electrons is not included because they are so small Every atom has a neutral charge because it has an equal number of protons and electrons.

Element Atomic Number Protons Electrons K 19 19 5 16 23 Short hand notation for writing the atomic mass and atomic number 12 C 6 13 C 6 14 C 6 What is the difference between these three carbon atoms. Is it a different number of protons, neutrons, or electrons? Isotopes: atoms that have the same number of protons but a different number of neutrons (different mass numbers) - Isotopes all have the same properties of that specific element

Radioactive Decay Isotopes containing a large number of neutrons give off energy called radiation. To become more stable radioactive isotopes break down in three different ways giving off three different types of radiation. - Alpha Radiation - Beta Radiation - Gama Radiation

Alpha Radiation Breaking down a radioactive atom to give off a helium atom. - This radiation is positive because it gives off a helium atom that contains two positive protons

Beta Radiation Breaking down a radioactive atom to give off an electron and a proton or hydrogen atom - This type of radiation is negative because it gives off an electron when the unstable isotope breaks down

Gamma Radiation Breaking down a radioactive atom to give off a helium atom and gamma rays - Gamma radiation is neutral because it gives off neutral gamma rays

What Radiation is Dangerous Alpha radiation gives off the least energy, beta gives off the second most, and gamma radiation gives off the most energy

Half-Life is the time required for one half of the nucleus of a radioactive isotope to break down. - Scientist use this information to identify how old a carbon sample is through carbon dating.

Atomic Mass: the average of all the masses of isotopes of an element - Is not a whole number like the mass of an individual atom - Atomic mass is based on the reference isotope Carbon-12. Atomic mass → Calculate the atomic mass of carbon if 2% of all carbon is Carbon-14, 6% of all carbon is Carbon-13, and 92% of all carbon is Carbon-12. Atomic mass =. 02 * 14 amu +. 06 * 13 amu +. 92 * 12 amu = 12. 1 amu

Development of the Periodic Table Mendeleev Constructed the first periodic table according to the similarities in each element’s properties - He arranged them in order of atomic masses - He left blank spaces in his periodic table because there were no known elements with the appropriate properties and masses.

Later Mosley rearranged the periodic table by atomic number The Modern Periodic Table Periodic Law: When elements are arranged in order of atomic number, there is a repetition of their physical and chemical properties

Groups or Families: vertical columns. Group numbers are indicated with a number and a letter A or B - Elements within a group have similar physical and chemical properties - Group A elements are the representative elements because they exhibit a wide range of chemical and physical properties

Where are things located on the Periodic Table? ← Nonmetals Metals → The light blue elements are semimetals

Properties of Metals: - They make up 80% of the elements - All metals except for one is a solid at room temperature - One the big periodic table solids are black, liquids are blue, and gases are red - They have a metallic luster - They are good conductors of electricity - They are malleable - They are ductile

Properties of Nonmetals - They lack luster - They are brittle - They are poor conductors of electricity (insulators) Properties of Semimetals - They have some of the characteristics of metals and some of nonmetals