Studied by 65 people
Experimented with a cathode ray tube and made a revolutionary discovery regarding the composition of atoms. Based on this observation he concluded that the ray must be composed of negatively charged particles.
This gave rise to a new atomic model called the "plum pudding model" where electrons are spaced throughout a spherical, positively charged medium.
Created the Gold Foil experiment, shooting a beam through the foil. There was a deflection, meaning there must be something very small, dense and positively charged in the center of an atom with electrons moving in an otherwise empty region around the outside.
This discovery led to the development of the first nuclear atomic model, the Bohr Model of the atom. Bohr re-imagined a nuclear model of the atom to be like a solar system with shells of electrons surrounding the nucleus.
Theorized in 1913:
Bohr's model shows electrons in specific "shells", also called energy levels.
Each atom has a specific number of these shells, and electrons with more energy are in shells further away from the nucleus.
A column on the periodic table, tells the amount of valence electrons and has similar properties
A horizontal row of elements in the periodic table, tells the amount of energy levels
Created the 5 postulates:
Elements are made of tiny particles called atoms
All atoms of a given element are identical
The atoms of a given element are different from those of any other element
Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and type of atoms.
Atoms are indivisible. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way atoms are grouped together.
Develops mathematical equations to describe the motion of electrons in atoms
His work leads to the electron cloud model
Also stated that electrons are not particles, but waves, so they cannot have a defined shape.
Dimitri Mendeleev
A Russian chemist known for creating the first widely recognized periodic table of elements, which organized elements by increasing atomic mass and predicted the properties of undiscovered elements. He is often referred to as the "father of the periodic table."
Henry Moseley
This British physicist established that elements should be arranged by the number of protons in the nucleus rather than by atomic mass. His work in the early 20th century corrected inconsistencies in the periodic table and laid the foundation for the current understanding of element properties and their relationships. He is known for Moseley's Law, which relates X-ray frequencies to atomic number.
Metals
Most elements are metals
Solids at room temperature, except Hg (liquid)
Malleable - can be bent without breaking
Ductile - can be stretched into wire
Lustrous - shiny
Good conductors of heat and electricity
High melting points
Nonmetals
Can be solids, liquids or gases at room temperature (depends on the element)
Solids are brittle - break easily
Dull-looking, but sometimes colored
Poor conductors of heat (insulators)
Poor conductors of electricity
Metaloids
Have some properties of metals and some of nonmetals
Solids at room temperature
Lustrous
Brittle - breaks instead of bending
Semiconductors - conduct electricity only under certain conditions
Alkali Metals
Group 1A (except H)
Most reactive metals
Metallic properties
React explosively with water
Never alone in nature
Alkaline Earth Metals
Group 2A
Very reactive (but less than alkali metals)
Metallic properties
Never alone in nature
Transition Metals
Groups 3B-2B
All are solids at room temperature (except Hg)
Metallic properties
Form cations with varying charges
Boron Group, Carbon Group, Nitrogen Group
Groups 3A, 4A, 5A
Properties vary due to containing metals, nonmetals, and metalloids
Oxygen Group
Group 6A
Often found in minerals with other elements
Halogens
Group 7A
Most reactive nonmetals
Means “salt former” because compounds with halogens form salts.
Highly Toxic
Exist in all 3 states of matter
(F and Cl are gases, Br is liquid, I and At are solid)
Noble Gases
Unreactive
Do not form compounds easily
Usually alone in nature
Often called “inert gases”
Lanthanides
Found in Period 6
(between barium and hafnium)
Highly reactive
Named for the element lanthanum
Actinides
Found in Period 7
(between radium and rutherfordium)
Highly reactive
Named for the element actinium
Elements after uranium (92) are synthetic (created by humans)
Representative/Main Group Elements
Group A
Inner Transition Metals/Rare Earth Metals
Lanthanide and Actinide Series
