Chemistry Unit 3: Atoms and Elements

Henry Moseley

Assigned each element an atomic number and created modern periodic table

Dmitri Mendeleev

-Maker of the first periodic table
-Incorrectly arranged elements by atomic mass

Groups

Vertical/1-18/similar properties

Periods

Horizontal/1-7/range of properties

Alkali Metals

Group 1/soft, shiny/good conductors/low melting point/highly reactive

Alkaline Earth Metals

Group 2/shiny/somewhat reactive

Halogens

Group 17/highly reactive/solids, liquids, gases

Noble Gases

Group 18/nonreactive/rarely found in combination with other elements

Elements

All mater is composed of elements

Four elements of everyday life

-Oxygen
-Carbon
-Hydrogen
-Nitrogen

Transition Metals

Group 3-12

Lanthanides

Period 6/57-71

Actinides

Period 7/89-103

Properties of Metals

-ductile (thin wires)
-malleable (thin sheets)
-luster(shiny)
-high melting points
-hard solids (besides mercury)
-good conductors

Properties of Nonmetals

-not ductile(no thin wires)
-not malleable(no thin sheets)
-not shiny
-low melting points
-gas, liquid, or solid
-poor conductors

Semimetals

-Elements with properties of both metals and nonmetals (metalloids)
-Categorized as semiconductors because can act as both conductor or insulator

Atoms

Smallest particle of element which still retains an elements characteristics

Atomos

A theorized idea from Greek Philosophers during 500 BC in which things divided and got smaller and smaller until they couldn't, and these indivisible atoms were specific to the material they composed

Dalton's Atomic Theory (1808)

-Atoms are indivisible (NOT TRUE) and indestructible and make up all elements
-Atoms of the same element are identical (NOT TRUE) & different elements have different properties & masses
-Compounds are formed when atoms of two or more elements combine in a whole number ratio
-Chemical Reaction involves rearrangement, separation, or combination of atoms & atoms can't be created or destroyed

Chemical Reactions

-A + B --> AB (Synthesis)
-AB --> A + B (Decomposition)
-AB + C --> AC + B (Single Replacement Reaction)
-AB + CD --> AC + BD (Double Replacement Reaction)

Subatomic Particles

-Protons (mass amu = 1.0)
-neutrons (mass amu =1.0
-electrons (mass amu = 1/1836)

Dalton's Atomic Model (1808)

Solid, indivisible sphere

Cathode Ray Experiment (1897)

-An experiment conducted by JJ Thompson in which he sent an electric current through a gas, and he applied a magnetic field to show that the particles were negatively charged
-His experiment found that electrons have electric charge and curve in a magnetic field, they have small mass, and required protons and neutrons

Thompson's Plum Pudding Atomic Model

Electrons in a diffuse positive cloud

Gold Foil Experiment (1911)

-Ernest Rutherford emitted positively charged particles through thin golden foil with the expectation that they would travel straight through, when some of the particles actually reflected because they repelled against the nuclei of the gold foil
-He concluded that the nucleus is the center of the atom, most of an atom's mass is the nucleus

Rutherford Atomic Model

Positive nucleus in the center surrounded by small randomly placed electrons with a great deal of empty space in between

James Chadwick

Discovered the neutron in 1932, found it was neutrally charged and had a mass approximately equal to a proton

Bohr Atomic Model

-Planetary model of atom in which electrons orbit the nucleus in a fixed pathway with fixed amounts of energy
-Only works with hydrogen because of one-electron system
-Does not explain bonding
Not proving effective

Schrödinger Atomic Model/Quantum Mechanical Model (1926)

-Erwin Schrödinger created the modern model of the atom
-Shows most probable location of an electron in a region called an orbital (electron cloud)
-Found that electrons also have heat-wave properties

Atomic Number

Number of protons and electrons

Mass Number

Number of protons and neutrons in nucleus (protons + neutrons = mass)

Nucleons

Name for protons and neutrons in an atom (number of nucleons = mass)

Isotopes

- Atoms of the same element that have the same atomic number but a different mass number
- Represented by atomic symbol
- Elements exist as mixture of isotopes
- Any given isotope has a fixed mass and certain abundance in nature