MATTER

WHAT IS MATTER? Anything that has mass and takes up space.

STATES OF MATTER Solids- tightly packed molecules, definite shape, does not conform to shape of container. Liquids- “slippery” molecules, definite volume, conforms to shape of container. Gases- lots of space between molecules, takes up all the volume of a container.

ELEMENTS Found on the Periodic Table Cannot be separated into smaller pieces and still retain the characteristics of the element.

COMPOUNDS Made of 2 or more elements chemically combined together. Have a FORMULA!

MIXTURES Two or more substances mixed together. NO chemical reaction has taken place! Can be separated by physical means.

HOMOGENEOUS MIXTURE Uniform in appearance No visible “chunks” Metal mixtures are alloys.

HETEROGENEOUS MIXTURES Not uniform in appearance Has visible “chunks”

Classify the following by element, compound or mixture Classify the following by element, compound or mixture. If the substance is a mixture, identify whether it is homogeneous or heterogeneous. NaCl 2. Kool-Aid Potting soil 14K gold Vegetable soup CaCO3 Magnesium sulfate Aluminum Hydrogen Creamy peanut butter

Basic Atomic Structure

EARLY THEORIES Democritus’s 460 – 370 B.C. Matter is composed of empty space through which atoms move. Atoms are solid, homogeneous, indestructible, and indivisible. Different kinds of atoms have different sizes and shapes. The differing properties of matter are due to the size, shape, and movement of atoms. Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves. Democritus’s ideas lost favor when he could not answer questions such as “What holds the atoms together?” Aristotle rejected Democritus’s ideas and his theories were lost for 2000 years.

Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton. John Dalton (1766-1844)

Dalton’s Postulates Each element is composed of extremely small particles called atoms. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

The Electron Streams of negatively charged particles were found to emanate from cathode tubes. J. J. Thompson is credited with their discovery (1897).

Millikan Oil Drop Experiment Robert Millikan (University of Chicago) determined the charge on the electron in 1909 [ – 1] and he calculated the mass of an electron [9.1 × 10-28 g]. Thomson now had the information he needed to propose his model of the atom that became known as “plum pudding model”

The Atom, circa 1900: “Plum pudding” model, put forward by Thompson. Positive sphere of matter with negative electrons imbedded in it. In 1911 Ernest Rutherford became interested in studying how positively charged alpha particles interacted with solid matter. He designed a famous experiment sometimes referred to as “gold foil experiment”

Discovery of the Nucleus Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.

The Nuclear Atom Since some particles were deflected at large angles, Thompson’s model could not be correct. This experiment suggested that the atom had a core of some sort – what we now call the nucleus

THE NUCLEAR MODEL According to Rutherford, most of the atom consists of electrons moving rapidly through empty space and a very dense, positively charged nucleus. Put the size of the nucleus in perspective; green pea in the center of a football field would be the nucleus and the rest of the field would be the “electron” space.

Other Subatomic Particles By 1920 , Rutherford had refined his concept of the nucleus: He concluded that the very dense nucleus contained positively particles called protons. James Chadwick, a coworker, showed that the nucleus also contained a neutral particle in 1932. This was the neutron – a particle with nearly equal mass as a proton.

Properties of Subatomic Particles Symbol Location Charge Relative mass Actual mass (g) Electron e- Around nucleus 1– 1 1840 9.11×10-28 Proton p+ Nucleus 1+ 1.673×10-24 Neutron n0 nucleus 1.675×10-24 Summary table – copy into notes

Atomic Structure and the Periodic Table Atomic number = # protons & # electrons (if neutral atom) 14 Si 28.086 Silicon Symbol Atomic Mass: Round to a whole #: 28 = Relative mass of nucleus 14 = # protons 14 = # neutrons Name

Practice From the Periodic Table Complete the following chart: Name Symbol Relative mass # protons # neutrons # electrons Lithium Mg 26 16