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Atoms, Elements, Compounds and Mixtures What is an atom? An atom is defined as the smallest particle of an element. John Dalton, a British School Teacher, proposed the atomic theory in 1802. He tested his ideas by carrying out experiments. What were some of Dalton’s ideas? In any element, all of the atoms are exactly alike. Atoms of different elements are different Atoms of each element have a unique mass. Daltons ideas are still used today and form the basis of our understanding of atoms How big are atoms? One grain of sand on a typical beach contains more atoms than there are grains of sand on the entire beach. There are about 2,000 billion billion (2,000,000,000,000,000,000,000) atoms of oxygen in a drop of water. Each dot of ink in a newspaper photo contains about a billion billion atoms (1,000,000,000,000,000,000) Particles… Protons Neutrons Electrons Subatomic Particles… Protons are positive + Neutrons are neutral Electrons are negative – Protons and neutrons are in the center of the nucleus Electrons are situated in electron clouds spinning around the nucleus – Valence Electrons – involved in the formation of chemical bonds – these are the outermost electrons in the electron cloud. These can be transferred or shared depending on the element IONS An ION is an atom or group of atoms that carry an electric charge. So…if an atom has more protons it is??? If there are more electrons?? What are elements? Elements are defined as a substance that cannot be broken down into any other substances by chemical or physical means. ***Elements are made up of atoms. Where do you find elements? EVERYWHERE!!!!!!!!!!!!! All of the matter in the universe is made from about 100 different elements. These elements are organized to form the Periodic Table of Elements. Some common elements are: Oxygen (O), Carbon (C), Hydrogen (H) and Gold (AU) Things to know… Atomic Number = the number of protons and electrons The difference between the atomic number and the atomic mass = the number of neutrons There has to be a pattern… There were only 55 elements known in 1830 – today we are up to over 100. Dimitri Mendeleev is the man responsible for organizing the Periodic Table as we see it today. It is organized in order of an increasing atomic mass. He also grouped elements that bonded alike and had similar properties – he even predicted a few. Organizing… Period: a row in the periodic table Group or Family: column on the periodic table – these all have similar properties – some are stronger than others… Atomic Number – the number of protons/electrons in element Atomic mass: average mass of elements atoms – usually increases with atomic number. Elements higher than 93 are artificially made Really high numbers like 114, 116, 118, etc – have Latin names relating to their location Classification… Groups are typically named based on the first element in the group: Example: Group14 is the Carbon family. Group 1 are metals that react violently with water, Group 11 reacts slowly with water, Group 17 reacts violently with Group 1, Group 18 doesn’t really react at all… The table works because it based on atoms – especially valence electrons. What are molecules? Molecules are defined as a combination of two or more atoms that are bonded together. Some molecules are made of atoms that are alike O2 (oxygen, the gas you breathe) two oxygen atoms combine. Other molecules are made of atoms that are different like H2O. BONDING… 2 primary kinds… IONIC – bonding of 2 oppositely charged ions (like magnets) - positive attracts negative and vice versa. NaCl is an ionic bond. Covalent – bond formed when 2 atoms share electrons – they are attracted at the same time. H2O is an example. What is a Compound? A compound is defined as a substance made of two or more elements chemically combined in a specific ratio. For example, carbon dioxide gas (CO2) is a compound made of one carbon atom and two oxygen atoms. What is the difference between molecules and compounds? A molecule is formed when two or more atoms join together chemically. A Compound is a molecule that contains at least two different elements. *All compounds are molecules but not all molecules are compounds. What is a mixture? A mixture is two or more substances (elements, compounds or both) that are together in the same place but are not chemically combined into a new substance. Soil is an example of a mixture because if you look closely you can see sand and clay in the soil sample. How does a mixture differ from a compound? Two ways: 1) Substances in a mixture keep their individual properties. 2) The parts of a mixture are not necessarily present in specific ratios. Atom, Molecule, or Compound ?? Atoms - smallest particle of an element Element – cannot be broken down by any means possible Molecule – 2 or more atoms that are bonded together. For example O2 and H2O. Compounds – substance made of 2 or more elements. For example: H2O ALL compounds are also molecules, BUT all molecules ARE NOT compounds… WHY??