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Changes in Matter - KGIC
Transcript of Changes in Matter - KGIC
Changes in Matter Review: Atoms and Molecules Changes in Matter:
Chemical Physical change - a change in the form of matter that does not make a new substance Atom - basic unit of matter; what matter is made of Molecule - a tiny unit of matter formed when atoms combine Combine - join together to make one Break/snap Rip/tear Melt Change in state = physical change Review: Changes in State Evaporate - to change from a liquid to a gas Condense - to change from a gas to a liquid Freeze - to change from a liquid to a solid Melt - to change from a solid to a liquid Form - the shape or structure of a substance Substance - something that has matter; something that has mass and takes up space Chemical Change - a change in matter that makes a new substance Physical and Chemical Changes
Worksheets Review: Parts of an Atom Solid Liquid Gas Burn / Combust - to change a substance using fire or heat Cook - to prepare food (changing the molecules) using fire or heat Prepare - to get ready Rust - when oxygen combines with iron to form a brown substance called "rust" (iron oxide) Corrode - to eat or wear away a substance by a chemical change State - what something is at a particular time (ex. solid, liquid, gas) Atoms have electron shells or energy levels. These are groupings or layers of electrons. Each shell can only have a maximum number of electrons. Maximum - the most or highest something can be The first shell (called "K"), can have a maximum of 2 electrons. When the outer shell is full, the atom is stable. Stable - not likely to change or react. For the first 20 elements, the maximum electrons in each shell, moving outwards, is 2, 8, 8, 2. A potassium atom looks like this: After that, the maximum electrons in each shell, moving outwards, is 2, 8, 18, 18, 32, etc. A gold atom looks like this: This helps us organize the Periodic Table: Remember: an element's atomic number is how many protons it has. Most elements will have a neutral charge, or the same number of protons (+) and electrons (-). +3 and -3 = 0 (neutral charge) The electrons in an element's outer shell are called valence electrons. Using the shell diagram, how many valence electrons does the element Carbon (C6) have? Worksheet: Valence Electrons Helium:
2 electrons Carbon has 4 valence electrons. Chemical Bonds - How atoms form molecules Most atoms want to be stable. Remember: an atom with a full outer shell of electrons is stable. Valence electrons can bond together with other atoms to form bonds. Bond - when two things join together When atoms share their electrons they form a chemical bond. This is how molecules are formed. A water molecule has two atoms of hydrogen and one atom of oxygen. It looks like this: H Worksheet: Chemical Bonds H is a chemical formula. This is a set of symbols used to show how many atoms are in a molecule. H = 2 hydrogen atoms
O = 1 oxygen atom What do you think the following formula means? CO CO
C = 1 atom of carbon
O = 2 atoms of oxygen 2 O 2 O 2 2 2 2 Chemical Reactions Remember! Some atoms have a neutral charge. This means there is __________________ number of protons and electrons. But...some atoms have _____________________
number of protons and electrons. These atoms are called ions. They have either a positive (+) or a negative (-) charge. Ion - an atom or molecule where the number of protons and electrons are different Positive charge (+) - when an atom or molecule has more protons than electrons. These ions are called cations. Negative charge (-) - when an atom or molecule has more electrons than protons. These ions are called anions. Remember! Atoms want to become stable. This means they have a full outer shell of electrons. Let's look at a neutral atom of oxygen:
It needs 2 more electrons (-) to become stable. Chemical reaction - the process of chemical change; when a change occurs and a new substance is formed Process - a number of actions happening one after another An oxygen ion, with a full outer shell, has gained 2 electrons. This means is has a negative charge of two (2-). A compound is a substance that is made from two or more elements.
Remember carbon dioxide (CO2)? Carbon dioxide is a compound. It is made from carbon and oxygen. What about sodium (Na)? A neutral atom of sodium has 11 protons and 1 valence electron:
When is loses its valence electron, it becomes an ion with a positive charge of one (1+). Sometimes ions can be made of more than one element. Some common ions with more than one element are below:
Ammonium: NH +
Nitrate: NO -
Carbonate: CO 2-
Cyanide: CN - There are two kinds of compounds: ionic compounds and covalent compounds. Ionic compounds - compounds made of metals and non-metals. They are formed when ions gain or lose electrons. Then the ions attract one another to form bonds. Let's go back for a minute...
There are two types of elements: metals and non-metals Metals - elements that are formed easily, conduct heat, and are often shiny Non-metals - elements that are not shiny and are poor conductors of heat. These elements are often gas, but not always. Conduct - to carry or guide Covalent compounds - compounds made of non-metals. They are formed when atoms share their valence electrons. Attract - to pull toward or near Periodic Table Worksheet - Ions Worksheet - Metals and Non-Metals 3 3 4