The Nature of Matter, Minerals, and the Periodic Table

Nature of Matter Matter = Anything that has mass and volume. (Mass is the quantity of matter in an object; volume is the amount of space matter takes up.) What is the difference between mass and weight???

Physical Properties of Matter Any characteristic of matter that you can observe and measure without changing the substances that make up the matter. Physical Property ALL matter can be described by its properties. Some physical properties describe a particular object: Iron Nail: Pointy-ended cylinder (shape); made of a dull, gray-colored solid (color & state of matter). Some physical properties can be measured: Nail is 2 inches (length), 1 gram (mass).

Physical Properties (cont.) Examples of physical properties: COLOR, SIZE, density, odor, volume, temperature, melting point & boiling point. Every substance has physical properties that distinguish it from other substances. Example: The substance IRON is attracted by a magnet.

Separating Mixtures A mixture is a combination that can be separated physically. The difference in a physical property can be used to separate substances in a mixture. How could you separate a mixture of cocoa pebbles cereal and lucky charms? Mechanically – boring, but possible How would you separate a mixture of iron filings and sand? Use a magnet – it will attract the iron filings and leave the sand behind.

Physical Changes Physical Change A change in size, shape, color or state of matter. Physical changes do not change the substances in a material. Physical Change If you break a piece of chalk, it loses its original size and shape (you’ve changed its physical properties). BUT… you have not changed the substances that make up the chalk. Changes of state are examples of physical changes – when water freezes, boils, evaporates, etc. (The state changes, but not the identity of the compound.)

Chemical Changes Chemical Change A change of one substance in a material to a different substance is a chemical change. There are many signs that can tell you when a chemical change has taken place: Foaming of an antacid tablet Smell in the air Production of energy/heat (exploding firecracker) Burning and rusting are chemical changes because different substances are produced.

Solids… SOLID Every solid has a definite shape and a definite volume! The molecules in a solid are held very close together. In elements- each element or mineral has a specific crystal shape. This crystalline shape determines properties for the element or mineral SOLID

Liquids… A liquid does not have a definite shape, but does have a definite volume! The molecules in a liquid are not held as closely together, so they can “slide” past each other. LIQUID

Gases… Gases don’t have a definite shape or volume – they expand or contract to fill the space available to them. The molecules in a gas are spread very far apart and can move in any direction. GAS

Elements All matter is made up of ATOMS (an atom is the smallest particle of an element). ELEMENT - When all the atoms in a sample of matter are the same. Examples: Carbon in a pencil point (C), Oxygen in air (O) and copper in a penny (Cu). Cu C O In total, there are 109 Elements.

Compounds Compounds: Made from atoms of two or more elements that are combined chemically. Compounds can only be separated through chemical means! Ex. NaCl- is table salt, but separately: Or maybe this one Examples: Water – made from the elements hydrogen and oxygen. Sugar – made from the elements carbon, hydrogen and oxygen. A molecule is the smallest particle of a compound.

Matter and Atoms Atoms are the basic building blocks of matter. Atoms have a positively charged center = nucleus. The nucleus contains protons and neutrons. All around the nucleus there are negatively charged particles = electrons. The mass of the electrons is much smaller than the mass of the protons and neutrons. Thus, most of the mass in an atom is located in the nucleus.

Protons, Neutrons & Electrons! A neutron is neutral; a proton is positively charged, and an electron is negatively charged. The nucleus is positively charged – why??? Comparison Of Particles In An Atom Particles Relative Mass Charge Location in Atom Proton 1 +1 Part of nucleus Neutron Electron -1 Moves around nucleus

Carbon = 6 Protons (+) and 6 Electrons (-) = ZERO CHARGE Atomic Number The atomic number of an atom is the number of protons in its nucleus. Example: Every carbon atom has 6 protons. This means its atomic number is 6 also! The number of electrons in an atom is equal to the number of protons. How many electrons does carbon have??? An atom is electrically NEUTRAL because it has the same number of protons and electrons. Carbon = 6 Protons (+) and 6 Electrons (-) = ZERO CHARGE

Atomic Number Carbon – Atomic Number is 6, which means it has 6 protons and also 6 electrons! Every atom of the same element has the same number of protons. Atoms of different elements have different numbers of protons – the periodic table is organized by increasing number of protons (increasing atomic number).

Mass Number Number of protons and neutrons in an atom. Mass Number = Protons + Neutrons Number of Neutrons = (Mass Number) – (Atomic Number) Sodium (Na) has 11 Protons and 12 Neutrons – What is its Mass Number? Mass number of Na = 11 + 12 = 23

Atomic Number & Mass Number (Protons + Neutrons) 23 Na Atomic Number (# of Protons and Electrons) 11 Na has 11 Protons, 11 Electrons, and 12 Neutrons.

Problem #1… 4 He 2 Which element does He stand for? Helium! How many protons does He have? Two! How many electrons does He have? How many neutrons does He have? Two! (Mass number - Atomic number = 4 - 2 = 2)

Problem #2… 12 C 6 Which element does C stand for? Carbon! How many protons does C have? Six! How many electrons does C have? How many neutrons does C have? Six! (Mass number - Atomic number = 12 - 6 = 6)

Models of the Atom A good model helps us understand something we cannot see – the atom! A good model must explain all of the information we have about the atom – as our information changes so must our models. Niels Bohr created one of the earliest models of the atom (1913).

Bohr Model of the Atom Bohr’s model had a central nucleus with electrons moving around it in defined paths or orbits. Why would this model also be called the Planetary Model of the Atom?

Electron Cloud Model of the Atom Improved Bohr’s model (1926). In this model, electron’s move around in an area called the electron cloud. It shows the region where an electron is likely to be (it is impossible to determine an exact location). Electrons are more likely to be closer to the nucleus than far away – this explains why the cloud is denser near the middle!