2 Some of the First Discussions about the Atom…. Democritus (400 BC) named the atom, which means indivisible, and said it was the smallest particle and could not be broken down.He was pretty much correct in that if you did break the atom down, it wouldn’t be that “element” any more. But he wasn’t aware that the atom was made up of particles.
3 Greeks Philosophers Continue the Discussion and Disagree Aristotle (350 BC) believed matter could always be broken down into smaller and smaller parts.And this is true to a certain extent… but eventually you come to the small basic particles that can no longer be broken apart.
4 His ideas are now called the Atomic Theory of Matter Dalton's Atomic TheoryIn 1808, John Dalton proposed that elements were composed of atoms & that only whole numbers of atoms can combine to form compoundsHis ideas are now called the Atomic Theory of MatterDalton’s Atomic Theory ( AD) was widely accepted but not totally correct
5 Dalton’s Atomic Theory All matter is composed of extremely small particles called atomsAtoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, & other propertiesELEMENT1ELEMENT2ELEMENT3ELEMENT4Dalton’s Atomic Theory
6 Atoms cannot be subdivided, created, or destroyed atoms of different elements combine in simple whole # ratios to form chemical compoundsin chemical reactions, atoms are combined, separated, or rearranged++
7 Not all of Dalton’s claims held up to the scrutiny of experimentation Atoms CAN be divided into even smaller particlesNot every atom of an element has an identical mass (isotopes are atoms of the same element, but with different mass numbers)Atomic Theory
8 Atomic Theory Dalton’s Atomic Theory of Matter has been modified. What remains is…All matter is composed of atomsAtoms of any one element differ in properties from atoms of another elementOne of the disputed statements of Dalton was that atoms are indivisible (we now know about protons, electrons, and neutrons)Atomic Theory
9 In the 1800’s it was determined that atoms are actually composed of several basic types of smaller particlesIt’s the number and arrangement of these particles that determine the atom’s chemical properties.A new definition of an atom is the one use today: the smallest particle of an element that retains the chemical properties of that original element.Atomic Theory
10 Plum Pudding ModelJJ Thomson’s cathode ray tube experiment in the late 1800s showed that atoms had smaller parts, called negative corpuscles; he developed the “plum pudding model.”The plum pudding model showed electrons (the plums) mixed in together with protons (the cake batter)
12 Scientists still didn’t really understand how the particles were put together in an atom. This was a difficult question to resolve, given how tiny atoms are.Most thought it likely that the atom resembled Thomson’s modelAtomic Structure
13 Rutherford’s gold foil experiment In 1911, Ernest Rutherford provided a more detailed picture of the internal structure of the atomHe showed that atoms had a nucleus where most of the mass resided.His model had a nucleus with a hard dense positively charged mass, negatively charged electrons outside, and that the atom was actually mostly empty space.
15 Bohr Model of the AtomNeils Bohr put electrons into different energy levels or shells.(This model is not correct either… electrons do not travel in orbits or paths like the model suggests)
16 Modern Day Theory (Electron Cloud Theory) The Modern Theory suggests that electrons are located somewhere in a cloud.
17 Basic and important fact to remember: All atoms contain the same basic parts, but atoms of different elements have different numbers of protons.The Periodic Table lists atoms in consecutive order by their Atomic NumberThe atomic number is directly related to the number of protons in the nucleus of each atom of that element
18 Atoms have: A nucleus small, dense part of the atom consists of protons and neutronsAn electron cloudlarge part of the atom that is empty space except for the electrons that are moving very fast and very randomly around the nucleusNucleusElectron Cloud
19 The total number of protons & neutrons determines the mass of the atom Called the “Mass Number” (atomic mass is the averaged mass of the isotopes and is given on the periodic table. Simply round the atomic mass to get the mass number)A Carbon atom, has 6 protons and 6 neutrons, so its mass number is 12If you know the atomic number & mass number of an atom of any element, you can determine the atom’s composition and the number of neutrons.
20 The Proton The protons are what give the atom its charge (+) They add mass to the atom as well. Each proton is equal to one AMU (atomic mass unit)The number of protons in an atom determines what element it is.The atomic number signifies the number of protonsProtons are held together in the nucleus by the “Strong Force” otherwise they would repel each other.
21 The Neutron The neutron adds mass (1 amu) to an atom but has NO charge Atoms of the same elements are identical due to the number of protons, but there can be different numbers of neutrons (we call those isotopes)To find the number of neutrons, subtract the atomic number from the mass number.
22 ElectronsElectrons have almost no mass, and we DO NOT count their mass.Located outside the nucleus in the electron cloud (aka: shells, orbitals, energy levels) moving at incredibly high speeds.Electrons have a negative (-) charge.Electrons found in the outermost shells of the atom are responsible for chemical reactions. Electrons have different amounts of energy depending what energy level they are at.Electrons can be removed and added to atoms quite easily, unlike protons.
23 Subatomic Particles Particle Symbol Charge Relative Mass Electron eProton pNeutron n
24 Location of Subatomic Particles 10-13 cmelectronsprotonsneutrons10-8 cmnucleus
25 in an atom and determines what element it is Atomic NumberCounts the numberof protonsin an atom and determines what element it is
26 Atomic Number on the Periodic Table 11NaAtomic NumberSymbolThe symbol represents the element. RULE: The first letter is always capitalized, and IF there is a second letter, it is lower case.
27 All atoms of an element have the same number of protons 11Na11 protonsSodium
28 Atomic Mass on the Periodic Table 11Na22.99Atomic NumberSymbolAtomic MassAtomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom. That is why there is a decimal.
29 Mass Number Counts the number of protons and neutrons in an atom (note: Atomic Mass is different from Mass Number. On your periodic table of elements, the atomic mass is usually given and you need to round it to the nearest whole number to use to figure Neutrons)
30 Atomic Notation atomic number 11 Show the mass number and atomic numberGive the symbol of the elementmass number23 Na sodium-23atomic number 11
31 Number of Electrons An atom is neutral when no charge is indicated. The net charge is zeroRemember: Atomic number = Number of protonsand therefore….Number of protons = Number of electrons when the atom is neutral.
32 Subatomic Particles Showing the P E N O P Zn8 p p+ 30 p+8 e e- 30 e-8 n 16 n 35 n
33 IsotopesAtoms with the same number of protons, but different numbers of neutrons.Atoms of the same element (same atomic number) with different mass numbersIsotopes of chlorine35Cl 37Clchlorine chlorine - 37
34 Learning CheckNaturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.12C C 14C#p _______ _______ _______#e _______ _______ _______#n _______ _______ _______