2Defining the Atom Essential Question How did the concept of the atom move from philosophy to science?
3Defining the AtomAn atom is the smallest particle of an element that retains its identity in a chemical reaction.
4Philosophy 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.
5Philosophy to ScienceGreater 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.
9Dalton’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.
10Dalton’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.
11Sizing 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.
12Sizing Up the AtomA line of 100,000,000 copper atoms side by side would be only 1 cm long.
13Sizing Up the AtomSizes 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!
14Sizing 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!
15Sizing Up the AtomIn Summary:Atoms are itty-bitty.
16Structure of the Nuclear Atom Atomic StructureStructure of the Nuclear Atom
17Structure 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?
18The 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.
19The Structure of the Nuclear Atom We will be most concerned with protons, neutrons and electrons.
20Subatomic Particles The Electron Discovered by ThomsonNegatively charged particlesRelative charge = 1–Symbol = e–1 / 1840 the mass of a protonReside outside of the nucleus
21Subatomic Particles The Proton Discovered by GoldsteinPositively charged particlesRelative charge = 1+Symbol = p+Mass of 1 atomic mass unit (amu)
22Subatomic Particles The Neutron Discovered by ChadwickNeutrally charged particlesRelative charge = 0Symbol = n0Mass of 1 atomic mass unit (amu)
28The Atomic NucleusThe nucleus is highly compacted and extremely dense.Most of the mass of atoms is in the nucleus.Nuclei have a density of about x 108 metric tons / cm3 !
29Distinguishing Among Atoms Atomic StructureDistinguishing Among Atoms
30Distinguishing Among Atoms Essential Question What part do protons, neutrons and electrons play in the identity and characteristics of atoms?
31Atomic NumberThe number of protons determines the identity of the element.The number of protons is indicated by the atomic number.
32Mass NumberThe 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?
33IsotopesIsotopes 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.
34Atomic MassMasses of atoms are incredibly small and impractical to express in gramsIt is more practical to compare the masses of atoms to a different standard.
35Atomic Mass UnitAn 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.
36Atomic MassAn 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.