THE BUILDING BLOCKS OF MATTER

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? ___________________________________________________________________________________________________

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.

WHAT DOES THE LAW STATE?

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 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?

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?

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

1. Matter made of extremely small particles called atoms

2. Atoms of an element are identical in: mass, size and other properties

3. Atoms cannot be subdivided, created or destroyed

4. Atoms combine in simple whole number ratios to for chemical compounds

5. 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

Today - 2010

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”; 1911What 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

Complete for homework

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?

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

Neutron-Neutron Attraction

The forces that hold the protons and neutrons together are referred to as NUCLEAR FORCES

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.

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

1. Two ways of writing isotopes:1. Hyphen notation: example:

1. Chlorine-37; uranium-235; carbon-14

2. Nuclear Symbol: example:1. 235 U the top number is the atomic

mass 92 and the bottom number is the atomic number

Top Top

number or number or

mass mass

number – number –

the the

bottom bottom

number or number or

atomic atomic

number = number =

the the

number of number of

neutronsneutrons

Formula

Example Find the number of protons, neutrons and electrons of: Chlorine-37:

Find the atomic number from the Periodic Table. The atomic number = Number of protons = number of electronsMass number = number of neutrons –atomic number

Atomic 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?

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

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 62.929599 amu and 30.83% of Copper-65 with atomic mass 64.927793 amu.

Calculating>.6917 X 62929599 amu

+ .3083 X 64.927793 amu = 63.55 amu

Example

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 6.022 X 1023 atoms

Examples: one molar mass of Lithium is 6.94 grams/moleOne molar mass of mercury (Hg) is 200.59 grams/mole

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 63.55 g/mol.

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 moles

The molar mass of aluminum from the periodic table is rounded to 26.98 g/mol.

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:

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 grams

The molar mass of copper from the periodic table is rounded to 63.55 g/mol.