Chemistry Topic 1

The Atom

• Chemistry – Mr. Sinto

• Topic 1 – The Atom

• Obj: SWBAT describe how our understanding of the atom has changed throughout time

• Do Now: What is Chemistry?

• Homework: Review Notes, Sign up for Remind, Get Syllabus signed.

• Chemistry – the study of matter

• Matter – anything that has mass and occupies space

Early Studies of Atoms

• Greeks – matter is composed of fire, air, water, and earth

• Dalton – the basic unit of matter is the atom

Dalton’s Theory

• All elements are composed of indivisible atoms

• All atoms of a given element are identical

• Atoms of different elements are different

• Compounds are formed by the combination of atoms of different elements.

Structure of the Atom

• Electrons

– JJ Thompson used a CATHODE RAY TUBE to discover electrons

– Negatively charged

Plum Pudding Model

• Negative charges embedded in atom

– Think chocolate chip

Gold Foil Experiment (ON EVERY REGENTS)

• Rutherford bombarded gold foil with alpha particles (positively charged)

• Results

– Most of the particles went straight through (MOST OF THE ATOM’S VOLUME IS EMPTY SPACE)

– Some were deflected and a few were reflected (SMALL, DENSE, POSITIVE NUCLEUS)

Gold Foil Experiment

Nucleus

• Protons – positively charged

• Neutrons – neutral

• Makes up most of the atom’s mass

– PROTONS AND NEUTRONS HAVE THE SAME MASS (1 amu)

– ELECTRONS ARE MUCH LESS

Bohr Model

• “Planetary model”

• Electrons found in shells outside nucleus

• OUTERMOST SHELL = VALENCE

• Electrons in valence shell = Valence electrons

• Noble gases (group 18) have a filled valence shell

Wave-Mechanical Model

• Modern theory of the atom

• Atom has dense positive nucleus

• Electrons found in orbitals

• ORBITAL = MOST PROBABLE REGION OF THE LOCATION OF AN ELECTRON

•EXIT TICKET

• Chemistry – Mr. Sinto

• Topic 1 – The Atom

• Obj: SWBAT explain the differences between the different subatomic particles

• Do Now: Where are protons, neutrons, and electrons found? What are their charges and masses?

• Homework: Review Notes, Sign up for Remind.

Subatomic Particles • Protons and Neutrons weigh 1 amu (atomic

mass unit)

• Electrons weigh much less

• ATOMIC NUMBER = NUCLEAR CHARGE = # OF PROTONS

• In a neutral atom, # protons = # electrons

Isotopes

• MASS NUMBER = # PROTONS + # NEUTRONS

• Samples of same elements have same # protons

• Isotopes = Same element, different mass number

– Same element, different number of neutrons

– Same # protons, different # neutrons

• Ex. O-16 and O-18, C-12 C-13 and C-14

•To find the number of neutrons

MASS # - ATOMIC #

Atomic Mass

• Weighted average of ALL NATURALLY OCCURRING ISOTOPES

• Take %, multiply by mass, add, then divide by 100

Location of Electrons

• Electrons are found in ORBITALS

• Electrons can gain or lose (fixed amounts of) energy to move between energy levels

• Gain Energy = Move up

• Lose Energy = Move down

– Losing energy and moving down gives off light

• Ground State – lowest available orbitals

– Found on the Periodic Table

• Excited State – When a lower level electron jumps to a higher level

– High Energy UNSTABLE

• Electrons in the ground state absorb energy and move to the excited state which is unstable. When they move back down to the ground state they release energy in the form of a bright line spectra

Bright Line Spectra

• If an element is in a mixture ALL OF ITS LINES MUST BE PRESENT

•EXIT TICKET

• Chemistry – Mr. Sinto

• Topic 1 – The Atom

• Obj: SWBAT differentiate between elements, mixtures, and compounds.

• Do Now: How do electrons produce light?

• Homework: STUDY

Types of Matter

• Homogeneous

– Uniform composition

– You can’t tell it’s individual parts

– Ex. Salt water, dissolved powder

• Heterogeneous

– Varying composition

– Can see individual parts

– Ex. Sand in water, pebbles in cement

Pure Substances

• Pure substances = composition is the same throughout

• Elements = SUBSTANCES THAT CANNOT BE BROKEN DOWN OR DECOMPOSED INTO SIMPLER SUBSTANCES BY CHEMICAL MEANS!!

• Compounds = two or more elements chemically combined in definite proportions

• Law of Definite Proportions

– Atoms in a compound exist in a fixed ratio

Mixtures

• Mixtures = combinations of two or more pure substances they CAN BE SEPARATED BY PHYSICAL MEANS

• Don’t have definite proportions

• Homogeneous mixture = SOLUTION

•EXIT TICKET