Atomic Structure Defining the Atom

Defining the Atom Essential Question How did the concept of the atom move from philosophy to science?

Defining the Atom An atom is the smallest particle of an element that retains its identity in a chemical reaction.

Philosophy or Science? Democritus believed that matter consisted of tiny, indivisible, unchangeable particles called atoms. Until recent centuries the existence of the atom was a philosophical question rather than a scientific one.

Philosophy to Science Greater accuracy in measurement allowed for experiments which indicated the existence of atoms. Law of Conservation of Mass, Law of Definite Proportions, and Law of Multiple Proportions were clues to the existence of atoms.

Dalton’s Atomic Theory 1) All elements are composed of tiny indivisible particles called atoms. 2) Atoms of one element are identical. The atoms of one element are different from those of any other element.

Dalton’s Theory (cont.) 3) Atoms of different elements can physically mix together, or can chemically combine in simple whole-number ratios to form compounds. 4) Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Sizing Up the Atom A copper penny contains about 2.4 x 1022 atoms. Earth’s population measures about 6 x 109 people. There are about 4 x 1012 times as many atoms in a penny as people on the earth.

Sizing Up the Atom A line of 100,000,000 copper atoms side by side would be only 1 cm long.

Sizing Up the Atom Sizes of atoms are expressed in picometers (trillionths of a meter). 1 cm is the same fractional part of 600 miles as 100 picometers is of 1 cm!

Sizing Up the Atom Dry air contains 0.002% Neon. Yet there are about 5 x 1017 atoms of Neon in every breath you inhale! That’s 500,000,000,000,000,000 atoms!

Sizing Up the Atom In Summary: Atoms are itty-bitty.

Structure of the Nuclear Atom Atomic Structure Structure of the Nuclear Atom

Structure of the Nuclear Atom Essential Question What are the three principle sub-atomic particles and what part do they play in the structure of the atom?

The Structure of the Nuclear Atom Atoms are known to be divisible. Sub-atomic particles include neutrinos, quarks, baryons, hadrons, fermions, bosons, mesons, leptons, photons, gravitons, gluons, electrons, protons and neutrons. Not to mention futons, croutons, Nissans and morons.

The Structure of the Nuclear Atom We will be most concerned with protons, neutrons and electrons.

Subatomic Particles The Electron Discovered by Thomson Negatively charged particles Relative charge = 1– Symbol = e– 1 / 1840 the mass of a proton Reside outside of the nucleus

Subatomic Particles The Proton Discovered by Goldstein Positively charged particles Relative charge = 1+ Symbol = p+ Mass of 1 atomic mass unit (amu)

Subatomic Particles The Neutron Discovered by Chadwick Neutrally charged particles Relative charge = 0 Symbol = n0 Mass of 1 atomic mass unit (amu)

The Atomic Nucleus Discovered by Rutherford (Gold Foil Experiment) The tiny central core of an atom Composed of protons and neutrons

The Atomic Nucleus The nucleus is highly compacted and extremely dense. Most of the mass of atoms is in the nucleus. Nuclei have a density of about 2 x 108 metric tons / cm3 !

Distinguishing Among Atoms Atomic Structure Distinguishing Among Atoms

Distinguishing Among Atoms Essential Question What part do protons, neutrons and electrons play in the identity and characteristics of atoms?

Atomic Number The number of protons determines the identity of the element. The number of protons is indicated by the atomic number.

Mass Number The mass number indicates the number of protons AND neutrons in the nucleus. How do you find the number of neutrons from the mass number of a given element?

Isotopes Isotopes are atoms of that have the same number of protons (the same element) but have different numbers of neutrons. They, therefore, have different mass numbers and different masses.

Atomic Mass Masses of atoms are incredibly small and impractical to express in grams It is more practical to compare the masses of atoms to a different standard.

Atomic Mass Unit An AMU (atomic mass unit) is defined as 1/12 the mass of a Carbon-12 atom. Since the Carbon-12 atom is made up of 6 protons and 6 neutrons, an AMU is approximately equal to the mass of one proton or one neutron.

Atomic Mass An element’s atomic mass is a weighted average mass of all the atoms in a naturally occurring sample of the element. To calculate atomic mass, multiply the mass of each isotope by its percent abundance (expressed as a decimal) and add the products.