Elements, Atoms and Compounds Earth Science 2.1A Matter Elements, Atoms and Compounds 9/6/2010

Matter Everything in the Universe is made of matter. 9/6/2010

Matter On Earth, matter exists usually in three states Solid: definite shape such as rocks Liquid: definite volume but no definite shape Gas: neither definite shape nor definite volume 9/6/2010

Matter Most of Earth’s atmosphere is composed of the gases nitrogen and oxygen 9/6/2010

Elements The names of many elements are common knowledge to us: gold, silver, copper, iron An element is a substance that can not be broken down into simpler substances by chemical or physical means. There are 112 known elements and new elements continue to be discovered to this day. 9/6/2010

Periodic table Elements have been organized into their know properties by a document called the periodic table of elements 9/6/2010

Atomic Number Each element is represented by a symbol with one, two or three letters Each element has it’s atomic number at the top The atomic number is the number of protons in the nucleus 9/6/2010

Periodic Table: periods & groups Rows across in the Periodic Table are called Periods The columns down in the Periodic Table are called Groups 9/6/2010

Periodic Table found in Earth’s Crust Of the know elements, only 8 make up the Earth’s crust Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium 9/6/2010

Atoms An atom is the smallest particle of matter that contains the characteristics of an element. The central region is called the nucleus The nucleus contains protons (+) and electrons (-) 9/6/2010

Protons, electrons, neutrons Protons are dense particles with positive (+) electrical charges Electrons have negative (-) charges and are smaller Neutrons are equally as dense as protons but have no charge, they are neutral in charge. 9/6/2010

Atoms Most atoms have the “same number of protons and electrons” balancing out their charge to a neutral charge. The positive and negative charges cancel each other out. For each proton their must be an electron to remain balanced. 9/6/2010

Atoms An electron is the smallest of the three fundamental particles in an atom An electron has a mass of about 1/1836 of a proton or neutron Electrons move about the nucleus so fast, that they create a sphere shaped negative zone, a cloud of negative charges called an electron cloud. 9/6/2010

Electrons Electrons are located in regions of this cloud called energy levels. Each energy level contains a “certain set number of electrons” 9/6/2010

Atoms: Mass Number The Mass Number of an atom is the total mass of the atom: the protons plus the neutrons Recall that the “mass of an electron” is so small that the number of electrons has no effect on the mass number of the atom. 9/6/2010

Atoms Not all atoms have equal numbers of protons and neutrons. Atoms with the same number of protons but different numbers of neutrons are isotopes of an element Isotopes of the same element are numbered using a convention called the mass number and with the elements name or symbol Iron-54 and Iron-57 are both isotopes of iron. 9/6/2010

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Nature of Matter: Atoms and Elements Biology 2.1 Nature of Matter: Atoms and Elements 1/30/2010

Nature of Matter All matter consists of atoms An atom is the smallest unit of matter that can not be broken down by chemical means. 1/30/2010

Atoms Atoms consist of three types of particles Electrons Protons Neutrons 1/30/2010

Electron Cloud The region around the nucleus that electrons may occupy at any time is called the electron cloud. Electrons move so fast in their orbits, they create a cloud of movement around the nucleus. 1/30/2010

Nature of Matter Electrons are negatively (-) charged so the electron cloud has a negative charge Protons are positively charged (+) Neutrons have no charge thus are neutral (0) 1/30/2010

Electrons, protons, neutrons Because protons and electrons are oppositely charged, they attract one another. Atoms typically have one proton for each electron so they cancel each other out and have no charge ( a neutral charge) 1/30/2010

Elements An element is a pure substance made up of only one kind of atom. There are more than 100 known elements and each is represented by a one, two, or three letter symbol. 1/30/2010

Table of the Elements Here is the Periodic Table Of Elements which shows the elements made up of one type of atom only! 1/30/2010

Elements Elements differ in the number of protons their atoms contain. Atoms of the simplest element, hydrogen, contain one proton and one electron. 1/30/2010

Elements The number of neutrons in a atom is often but not always equal to the number of protons in the atom. Atoms of an element that contain different numbers of neutrons than protons are called isotopes. 1/30/2010

Elements We can model isotopes of the elements using magnets. Material A non-magnetic tabletop. 1 disk magnet with one color, mine are painted white 2 disk magnets with a different color, mine are painted black, both sets of magnets should be the same size. 1/30/2010

Elements Deuterium To Do and Notice The white magnet represents the proton and the black ones neutrons. Place one proton on the table. This is the nucleus of hydrogen. See the image at right. Normally, hydrogen does NOT have a neutron! It is the simplest atom. 1/30/2010 Deuterium

Elements Deuterium To Do and Notice Hydrogen has a stable isotope named deuterium, 2H, or 2D, with one proton and one neutron. This represents a stable isotope. The proton and neutron numbers are the same but normally hydrogen has NO neutron! Therefore, this is an isotope but a stable one. 1/30/2010 Deuterium

Elements Hydrogen has a radioactive isotope named tritium, 3H, with one proton and two neutrons. Place one white and two black magnets on the table so that the white magnet attracts both black magnets. 1/30/2010

Elements The row at the right represent the nucleus of tritium. Here we see the white washer representing a proton with a positive charge. The two black washers represent the two neutrons. The extra neutron shifts it from a stable isotope to a radioactive unstable isotope. 1/30/2010

Chemical Bonding Atoms can join together with other atoms to form stable substances. A compound is a substance made of the joined atoms of two or more different elements. 1/30/2010

Covalent Bonds Covalent bonds form when two or more atoms share electrons to form a molecule. Covalent bonding occurs in ceramics, glass, wood and other organic materials. When atoms bond using covalent bonding, the atoms share electrons in their outer shell creating full shells for both. 1/30/2010

Covalent Bonds Covalent bonds give a very strong bond. Diamond is a good example of a strong covalent bond and has a high melting point and is very hard. A molecule is a group of atoms held together by covalent bonds. 1/30/2010

Ionic Bonds Sometimes atoms or molecules gain or loose electrons. An atom or molecule that has gained or lost one or more electrons is called an ion. 1/30/2010

Ionic Bonds Ions have an electrical charge because they contain an unequal number of protons and electrons. An atom that has gained electrons is negatively charged (-). It has more electrons (-) than protons (+) An atom that has lost electrons is positively charged (+). It has more protons (+) than electrons. (-) 1/30/2010

Ionic Bonds Ions of opposite charge may interact to form an ionic bond. An ion with an extra electron (a negative charge) will be attracted to an ion with more protons than electrons ( a positive charge). For both to become stable, the negative ion with more electrons (-) will be attracted to the positive ion that needs electrons (+) and seek to give away it’s extra electrons. 1/30/2010

Ionic Bonds This attraction of ions of opposite charge interacting to transfer electrons is an ionic bond. 1/30/2010

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