Matter & The Atom

Matter  The term matter describes all of the physical substances around us  Anything that has mass and volume (takes up space)  The Universe is made up of matter and energy (light, sound, and heat are not made of matter)

Matter is made of atoms Atoms are the building blocks of matter An atom is the smallest whole particle of matter Sub-atomic particles are tiny particles that make up an atom

Models Models are often used for things that are too small or too large to be observed or that are too difficult to be understood easily

Models In the case of atoms, scientists use large models to explain something that is very small How small are atoms? Models of the atom were used to explain data or facts that were gathered experimentally. So, these models are also theories

Early Models of the Atom Democritus He asked: “What would happen if you took something (like a tree) and kept breaking it into smaller and smaller pieces? Would it still be a piece of a tree? Could you keep breaking it? He concluded: Eventually you would get to a size that could no longer be broken. This would be an indivisible piece Greek word: atomos = indivisible Thus: ATOM (442 B.C.)

Early Models of the Atom John Dalton (1803) All elements are composed of indivisible particles. Atoms of the same element are the same Atoms of different elements are different. Different elements are atoms with different masses

Early Models of the Atom J.J. Thomson (1897) Found negative and positive charges Plum pudding model Atom made of a positively charged material with the negatively charged electrons scattered through it.

Early Models of the Atom Ernest Rutherford (1899) Mostly empty space Small, positive nucleus Contained protons Negative electrons scattered around the outside

Early Models of the Atom Niels Bohr (1915) Electrons are small and negatively charged Electrons move in definite orbits around the nucleus (energy levels) Protons are in the nucleus and the nucleus is small compared to the atom

Early Models of the Atom James Chadwick (1932) Discovered the neutron

Modern Model of the Atom The electron cloud Spherical cloud of varying density Varying density shows where an electron is more or less likely to be

Atomic Structure Nucleus –Protons –Neutrons Electrons

Atomic Structure Nucleus The center of the atom –Contains protons and neutrons All particles are inside or around the nucleus

Atomic Structure Electrons (e - ) Tiny, very light particles –Smallest subatomic particle Have a negative electrical charge (-) Found in a cloud outside of the nucleus Orbits in energy levels

Atomic Structure Protons (p + ) Located in the nucleus of the atom Much larger and heavier than electrons Protons have a positive charge (+) Number of protons is different for each element. If the number of protons changes, the element changes.

Atomic Structure Neutrons (n 0 ) Located in the nucleus of the atom Large and heavy like protons, a bit bigger than a proton Neutrons have no electrical charge (neutral)

Relative size of sub-atomic particles

Atomic Structure proton (p+) neutron (n o ) electron (e-)

Describing Atoms Atomic Number = number of protons –In a neutral atom, the # of protons = the # of electrons –All atoms want to be neutral (no electrical charge)

ElementAtomic ## protons Hydrogen11 Gold79 Oxygen8 Iron26 Lead82 Helium2 Sodium11 Sulfur16

Describing Atoms Atomic Mass Number - sum of the number of protons plus neutrons. –Electrons are so tiny that their mass isn’t enough to affect the atomic mass Measured in Atomic Mass Units (amu)

Isotopes Isotope – when an atom has a different number of neutrons than other atoms of the same element –Example: 2 Oxygen Atoms, one has 8 neutrons one has 9.

Isotopes, continued The number of protons for a given atom never changes. The number of neutrons can change. Two atoms with different numbers of neutrons are called isotopes Isotopes have the same atomic # Isotopes have different atomic Mass #’s