SCIENCE 2Q reviewer

SCIENCE REVIEWER

Atomic theory

• A scientific concept that explains the nature of matter and its behavior.
• Evolved over centuries with contributions by other/of many scientists.

Scientist’s atomic model:

1. Dalton - solid sphere model
2. Thomson - plum pudding/blueberry muffin model
3. Rutherford - nuclear model
4. Bohr - planetary model
5. Schrodinger - quantum model

Atomism

• A theory that was first proposed by the Ancient Greek Philosopher, Democritus.
• All matter is made up of tiny, indivisible particles called “atoms” or “atomos”, which are in constant motion.

Solid Sphere model

• Made by Dalton
• Revived Democritus’ theory
• Believed that atoms of the same element are identical in their properties
• Atoms cannot be subdivided

3 fundamental laws:

1. Law of Convervation of Mass

• States that in a chemical reaction, the total mass of the reactants is equal to the mass of the products.
• The numbers of atoms are conserved, but they are rearranged during a reaction and thus their total mass is the same before and after a reaction.

1. Law of Definite Proportions

• States that a pure substance is composed of the same elements in the same proportions by mass regardless of the source of the substance.

1. Law of Multiple Proportions

• States that when two elements combine to form more than one compound, the mass of one element that combines with a fixed mass of the other element is always whole-number ratios.

Plum Pudding model

• Made by Thomson
• Used the Cathode Ray Tube Experiment to discover the electrons
• Had the idea that the empty space is positively charged
• Also known as the “plum pudding” or “blueberry muffin” model

Nuclear model

• Made by Rutherford
• Positively charged nucleus w/ electrons orbiting it
• Also known as the “cherry with a pit” model
• Atom is mostly empty space
• Discovered the nucleus using the Alpha Particle/Gold Foil Experiment

James Chadwick

• Discovered the neutron of an atom

Planetary model

• Made by Bohr
• Electrons are held in their orbits (energy level) by electrostatic forces
• Each electron is confined to a specific orbit

Line Spectrum

• Consists of specific discrete line on a background

Quantum Mechanic model

• Made by Schrodinger
• Described the probability of finding electrons within given orbitals, or 3D regions of space, within an atom.
• Electrons are confined to a space in an orbit
• Electrons move at a high speed which makes an electron cloud
• Is also known as the “cotton ball” model
• Electrons within atoms could be explained mathematically by treating them as matter waves

Energy levels/electron shells

• Each shell can only accommodate a limited number of electrons.

Subatomic Particles:

1. Protons
2. Neutrons
3. Electrons

Subatomic : Sub = under/inside

Atomic = atom

Electrons

• Are on energy shells
• Outside the nucleus

Protons and Neutrons

• Have basically the same mass
• Inside the nucleus

Atomic Number

• Number of protons
• Protons only

Atomic Mass

• Number of protons and neutrons
• Also known as “atomic weight” or “mass number”
• Protons + neutrons

Number of protons

• Dna of an atom
• Does not change
• Tells the so-called “identity” of an element
• Does not participate in chemical change

Neutral Atom

• Neutron is equal to the electron
• An element that has no charge
• Protons = electrons

Ions

• Charged particles
• Have 2 types:

- positively charged ion = cation

- negatively charged ion = anion

Cation

• Donates electrons

Anion

• Accepts electrons

Periodic table

• Organizes the elements in a particular way

Johann Wolfgang Dobereiner

• The first developer of the periodic table
• Developed the law of triads

Law of Triads

• The atomic mass of the middle element was approximately equal to the average mass of the heaviest and the lightest ones

Dmitri Mendeleev

• The first to arrange the periodic table
• Developed the original periodic table
• Was the first to notice the relationship between the elements
• Arranged his periodic table by atomic mass
• Noticed that there were repeated properties that reoccur in a periodic pattern or “periodicity”
• Was known as the Father of the Periodic Table due to his prediction

John Newlands

• Made the “law of octaves”
• Noticed that every eighth element exhibited similar properties

Law of octaves

• Every eighth element exhibits similar properties in the periodic table

Julius Lothar Mayer

• Arranged the elements in increasing atomic mass
• Was the first to recognize the periodic trends in the elements

Henry Moseley

• Is responsible for the creation of the modern periodic table
• Elements should be arranged according to their atomic number
• Fixed the inconsistencies of Mendeleev’s periodic table
• Grouped the elements by their properties in a vertical column
• Added a new column called noble gases

Periods

• Number of orbits in an atom
• Are horizontal rows on the periodic table
• Elements in the same period have consecutive atomic numbers
• Have the same number of energy shells/energy level
• Numbered from 1-7

Groups

• Are the vertical columns in the periodic table
• Elements of the same group usually have similar properties
• Elements of the same group have the same valance electrons
• Numbered from 1-18
• Not all of the groups follow the valance electrons

Valance electrons

• Are the electrons in the outermost energy level

Representative elements (A Group)

• Have predictable properties
• Groups 1&2 and 13-18

B Group

• The other elements
• The transition metals (the isolated elements are the inner transition metals)
• Have unpredictable properties

Special names of the representative elements:

1. Group IA - alkali metals
2. Group IIA - alkaline earth metals
3. Group VIIA - Halogens
4. Group VIIIA - noble gas

Alkali Metals

• Have a silvery appearance and are soft enough to cut with a knife
• Very reactive so they cannot be found in nature as free elements

Alkaline Earth Metals

• Harder, denser, and stronger than alkali metals
• Less reactive than alkali metals

Halogens

• Gases that are the most reactive nonmetals
• Reacts vigorously with most metals to form compounds

Noble Gas

• Do not react with other elements on the periodic table
• Do not need other elements to exist
• Chemically inert

Atomic Diagram

Metals

• Are generally hard and lustrous
• The only nonsolid metal that is liquid at room temperature is mercury
• Are good conductors of electricity and heat

Malleable

• Can be hammered or flattened into thin sheets

Ductile

• Can be drawn into thin wires without breaking

Nonmetals

• Generally exist as gases or solids in nature
• The only liquid nonmetal is bromine
• Because of their brittleness, they are neither malleable nor ductile

Metalloids

• Are elements that possess the properties of both metals and nonmetals
• A brittle solid that can conduct a limited amount of electricity is silicon