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Presentation on theme: "THE BUILDING BLOCKS OF MATTER"— Presentation transcript:


2 Do Atoms Exist? Democritus – First person known to suggest that matter can be broken down into small particles that he named: ATOMS In 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 conservation From 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 Proportions Other example: Carbon dioxide is always 1 Carbon and 2 Oxygen atoms Carbon Monoxide is always 1 Carbon and 1 Oxygen atoms Hydrogen Peroxide is always 2 Hydrogen and 2 Oxygen atoms What 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 proportions What 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 numbers 2:1, 3:1, 3:2, etc…. In the examples below, find the whole number ratio between: C2H2 and C2H6 H2O2 and H2O

8 Dalton's Theory Vs. Modern Theory of the Atom
Today Dalton’s Atomic Theory year 1808 Matter made of extremely small particles called atoms Atoms of an element are identical in: mass, size and other properties Atoms cannot be subdivided, created or destroyed Atoms combine in simple whole number ratios to for chemical compounds In chemical reactions, atoms combine, separate or are rearranged Statement 1, 4 and 5 are still accepted today Statement 2 has been modified because we now know that atoms of an element can differ. A given element can have atoms of different masses Statement 3 is incorrect. Atoms can be subdivided and have been

9 How were the Particles of the Atom Discovered?
Discovery of the Electron Discovery of the Nucleus & Proton Discovery of the Neutron Discover/Experimenter: Joseph John Thomson Discover/Experimenters: Ernest Rutherford, Hans Geiger and Ernest Marsden Discover/Experimenter: Chadwick Experiment/year: Cathode Tube; 1897 Experiment/year: commonly known as “Rutherford’s experiment”; 1911 What was his greatest discovery and what was the controversy this created among scientists? Experiment/year: Complete for homework Showed: 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 electrons Showed: 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 Attraction Protons are closely packed at the center of the atom When protons are extremely close, there is a STRONG ATTRACTION between them. More than 100 protons can exist close together in the nucleus Similar attraction between neutrons in the nucleus The forces that hold the protons and neutrons together are referred to as NUCLEAR FORCES

12 Atoms electron Mass: Charge: Proton neutron Charge radius of atoms: 40 to 270 pm (4.0 X 101 pm to 2.70x 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.

13 Counting Atoms

14 Protons Neutrons Electrons The 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 number The 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 number The number of electrons is equal to the atomic number when the atom is neutral Mass 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-14 Nuclear Symbol: example: 235 U the top number is the atomic mass and the bottom number is the atomic number Formula Top number or mass number – the bottom number or atomic number = the number of neutrons Example Find the number of protons, neutrons and electrons of: Chlorine-37:

16 Solution Find the atomic number from the Periodic Table. The atomic number = Number of protons = number of electrons Mass number = number of neutrons –atomic number Atomic number from the Periodic Table = 17 The number of electrons is = 17 The 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 Unit The 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 units One atomic mass unit or 1 amu is 1/12 the mass of a carbon-12 amu

18 Calculating Average Atomic Mass
Example Weighted average of the atomic masses of the naturally occurring isotopes of an element Copper 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 or 6.022 X 1023 particles in one mole of a pure substance The 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 carbon Example: one mole of copper has X 1023 atoms Examples: one molar mass of Lithium is 6.94 grams/mole One 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 Cu Unknown: mass of Cu in grams Solution: 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 Al Unknown: amount of Al in moles The 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 Ag Unknown: amount of Ag in moles Solution:

24 What is the mass in grams of 1.20  108 atoms of copper, Cu?
Given: 1.20 × 108 atoms of Cu Unknown: mass of Cu in grams The molar mass of copper from the periodic table is rounded to g/mol.


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