Presentation on theme: "THE BUILDING BLOCKS OF MATTER"— Presentation transcript:
1 THE BUILDING BLOCKS OF MATTER ATOMSTHE BUILDING BLOCKS OF MATTER
2 Do Atoms Exist?Democritus – First person known to suggest that matter can be broken down into small particles that he named: ATOMSIn the 1790s, chemists are using better instruments and are able to make better measurements.Using these instruments, theories about matter are developed. Some of which are still valid today.In the late 19th century and early 20th century, some fundamental discoveries were made about the atom due to the further development of instruments.What did Einstein propose? __________________________________________________ _________________________________________________Show burning of sugar or hcl + zinc - show video of Boltzman and Einstein
3 What happens to Atoms When a Chemical Change Happens? Show other three dimensional examples of the law of conservationFrom illustration, what can we determine about what happens to the particles before and after a chemical reaction?
4 WHAT DOES THE LAW STATE?Mass is neither destroyed nor created during ordinary chemical reactions or physical change.Example:If you have 50 grams of matter before a chemical reaction or physical change, the total mass will be 50 grams after the chemical reaction or physical change.
5 How do Atoms Combine in a Compound? What is the formula for water?A chemical compound contains the same elements in exactly the same proportions by mass even if the size of the samples change. It is the law of Definite ProportionsOther example:Carbon dioxide is always 1 Carbon and 2 Oxygen atomsCarbon Monoxide is always 1 Carbon and 1 Oxygen atomsHydrogen Peroxide is always 2 Hydrogen and 2 Oxygen atomsWhat is the ratio of elements in Hydrogen Peroxide and how is that different from Water?Show model of the molecules
6 Law of Multiple Proportions Show other three dimensional examples of multiple proportionsWhat is different between the two examples?What is the same?What is the ratio between the mass of Oxygen in the first example and that in the second example?
7 What does the Law Say?If we have two different substances that have the same two elements, if we combine the second element with the same amount of the first, the ratio of the elements are always small whole numbers2:1, 3:1, 3:2, etc….In the examples below, find the whole number ratio between:C2H2 and C2H6H2O2 and H2O
8 Dalton's Theory Vs. Modern Theory of the Atom TodayDalton’s Atomic Theoryyear 1808Matter made of extremely small particles called atomsAtoms of an element are identical in: mass, size and other propertiesAtoms cannot be subdivided, created or destroyedAtoms combine in simple whole number ratios to for chemical compoundsIn chemical reactions, atoms combine, separate or are rearrangedStatement 1, 4 and 5 are still accepted todayStatement 2 has been modified because we now know that atoms of an element can differ. A given element can have atoms of different massesStatement 3 is incorrect. Atoms can be subdivided and have been
9 How were the Particles of the Atom Discovered? Discovery of the ElectronDiscovery of the Nucleus & ProtonDiscovery of the NeutronDiscover/Experimenter: Joseph John ThomsonDiscover/Experimenters: Ernest Rutherford, Hans Geiger and Ernest MarsdenDiscover/Experimenter: ChadwickExperiment/year: Cathode Tube; 1897Experiment/year: commonly known as “Rutherford’s experiment”; 1911What was his greatest discovery and what was the controversy this created among scientists?Experiment/year:Complete for homeworkShowed: existence of a negatively cathode ray; the ray had mass and force; ray deflected by magnetic field and negatively charged objects; all cathode rays composed of negatively charged particles that were later named electronsShowed: existence of a nucleus with positive particles. A thin piece of gold foil was bombarded with a narrow beam of alpha (+) particles. Some of the particles were redirected by the gold foil back toward the source. Rutherford’s hypothesis: negatively charged electrons surround positively charged nucleus
10 What are Scientists Certain About the Atom What is the difference between the charge of a proton and an electron?Which particle has the least mass? By how much less?Which of them is neutral and where is it located?
11 Strong Nuclear Forces Proton-Proton Attraction Neutron-Neutron AttractionProtons are closely packed at the center of the atomWhen protons are extremely close, there is a STRONG ATTRACTION between them. More than 100 protons can exist close together in the nucleusSimilar attraction between neutrons in the nucleusThe forces that hold the protons and neutrons together are referred to as NUCLEAR FORCES
12 AtomselectronMass:Charge:ProtonneutronChargeradius of atoms: 40 to 270 pm (4.0 X 101 pm to2.70x 102 )Radius of nucleus: pm (1 x pm)Why is matter mostly empty space? Hint: look at the radius difference between the atomic radius and nucleus radius)Homework: Are there other sub particles in the atom? If there are, give some examples.
14 ProtonsNeutronsElectronsThe atomic number of an element represents the number of protons . The atomic number (Z) is the same for all atoms of a specific element.For example, all Hydrogen atoms have 1 proton, all helium atoms have 2 protons. Elements are listed in the periodic table according the atomic numberThe number of neutrons can differ in atoms of the same element. For example: Hydrogen-2 (Deuterium) has 1 neutrons while Hydrogen-3 has 2 neutrons.Helium-3 has 1 neutron and Helium-4 has 2 neutrons.These examples above are called ISOTOPES or atoms of the same element with different masses.# of neutrons = mass number – atomic numberThe number of electrons is equal to the atomic number when the atom is neutralMass number is equal to the total number of protons and neutrons or the atomic number + the number of neutrons
15 Formula Two ways of writing isotopes: Hyphen notation: example: Chlorine-37; uranium-235; carbon-14Nuclear Symbol: example:235 U the top number is the atomic massand the bottom number is the atomic numberFormulaTop number or mass number – the bottom number or atomic number = the number of neutronsExample Find the number of protons, neutrons and electrons of: Chlorine-37:
16 SolutionFind the atomic number from the Periodic Table. The atomic number = Number of protons = number of electronsMass number = number of neutrons –atomic numberAtomic number from the Periodic Table = 17The number of electrons is = 17The number of neutrons is:37 – 17 protons = 20 neutrons.Calculate:How many protons, neutrons and electrons are there is atom of bromine-80?
17 Atomic Mass UnitThe standard used by scientists to apply to atomic mass is based on an atom: carbon-12 nuclide.The mass assigned to this nuclide is 12 atomic mass unitsOne atomic mass unit or 1 amu is 1/12 the mass of a carbon-12 amu
18 Calculating Average Atomic Mass ExampleWeighted average of the atomic masses of the naturally occurring isotopes of an elementCopper has two naturally occurring isotopes:69.17% of Copper-63 with a mass of amu and 30.83% of Copper-65 with atomic mass amu.Calculating>.6917 X amu X amu = amu
19 Three Ways to Count The Mole Avogadro’s Number Molar Mass Like a dozen, the mole represents a certain amount of a substance.The number of particles in a mole or6.022 X 1023 particles in one mole of a pure substanceThe mass of one mole of a pure substance in grams. It is equal to the atomic mass that we find in the periodic table for each element.Example: for example, number of carbon has 12 grams of carbonExample: one mole of copper has X 1023 atomsExamples: one molar mass of Lithium is 6.94 grams/moleOne molar mass of mercury (Hg) is grams/mole
21 What is the mass in grams of 3.50 mol of the element copper, Cu? Given: 3.50 mol CuUnknown: mass of Cu in gramsSolution: the mass of an element in grams can be calculated by multiplying the amount of the element in moles by the element’s molar mass.The molar mass of copper from the periodic table is rounded to g/mol.
22 A chemist produced 11. 9 g of aluminum, Al A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced?Given: 11.9 g AlUnknown: amount of Al in molesThe molar mass of aluminum from the periodic table is rounded to g/mol.
23 How many moles of silver, Ag, are in 3.01 1023 atoms of silver? Given: 3.01 × 1023 atoms of AgUnknown: amount of Ag in molesSolution:
24 What is the mass in grams of 1.20 108 atoms of copper, Cu? Given: 1.20 × 108 atoms of CuUnknown: mass of Cu in gramsThe molar mass of copper from the periodic table is rounded to g/mol.