LaGreca ScienceUnit 2Chemistry Study Guide

UNIT 2 STUDY GUIDE

CHEMISTRYPart 1: Matter is made up of atoms which then is composed of elements (6.P.2.1)

Question: What is matter and what is it made up of? How is it possible for matter to have different properties?

All substances, including air, take up space and have mass.

Matter is everything around you. Matter is anything that has mass and takes up space.

The smallest unit of matter is an atom. The ancient Greeks found no smaller particles and therefore called the particles they found “atoms” which means “uncuttable” in Greek.

Atoms are the building blocks of life. Atoms come together in different ways to form elements. Atoms of different elements have different masses. Most atoms of the same elements have the same masses, except for isotopes, but you don’t need to know about them this year!

Property-specific characteristics of matter. Some properties are physical, and some properties are chemical in nature.

Atoms of the same element have the same properties (specific characteristics).

Atoms of different elements have different properties.

Elements come together to form molecules. Common elements can form to build very different molecules. There are 120 different elements that come together to form millions of different molecules . Two samples of the same substance contain the same type of atoms and elements!

Every atom of an element has both mass and volume! The measure of the gravitational force of an object is called the weight. Different substances of the same size wll most like have a different mass. For example, compare the mass of a tennis ball vs. a lacrosse ball of the same size and dimensions.

Molecules are groups of atoms bonded together in a way that letters are grouped together to form words. They are connected together by chemical bonds. Every combination of atoms is a molecule

A compound is a molecule made of atoms from different elements. Can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means). Has properties that are different from its component elements

Example: Water (H2O)

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LaGreca ScienceUnit 2Chemistry Study Guide

*** All compounds are molecules, but not all molecules are compounds. Hydrogen gas (H2) is a molecule, but not a compound because it is made of only one element. Water (H2O) can be called a molecule or a compound because it is made of hydrogen (H) and oxygen (O) atoms.

Mixture- A physical change, not a chemical change. Consists of two or more different elements and/or compounds physically intermingled, can be separated into its components by physical means, and often retains many of the properties of its components.

Example: Salt and water (NaCl and H2O)

Solution- A type of mixture where groups of molecules that are mixed and evenly distributed in a system. Scientists say that solutions are homogenous systems. Everything in a solution is evenly spread out and thoroughly mixed.

Solutions can be solids dissolved in liquids. Solutions can also be gases dissolved in liquids, such as carbonated water. There can also be gases in other gases and liquids in liquids. If you mix things up and they stay at an even distribution, it is a solution. You probably won't find people making solid-solid solutions.

Periodic table of elements-a big grid that organizes the elements according to its atomic structure. The rows are called “periods” and the columns are called “groups”

Elements are numbered according to their atomic number, which tells you how many protons an atom has. (Note 6th graders do NOT need to know proton, neutron or electrons )

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LaGreca ScienceUnit 2Chemistry Study Guide

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Part 2: Identify and explain the changes in the states of matter and their properties of change (6.P.2.2)

Questions: What are the different phases of matter? How does matter behave during these different phase changes?

Matter can have different chemical and physical properties

Molecules can move from one physical state to another (phase change) and not change their basic structure. It has the same molecular structure whether it is a gas, liquid, or solid. Although its physical state may change, its chemical state remains the same.

Physical change: when matter experiences a change in arrangement of molecules, such as in a phase change, without changing the chemical structure (the elements remain the same)

Changes in the physical state are related to changes in the immediate environment such as temperature, pressure, and other physical forces. Generally, the basic chemical structure does not change when there is a physical change. Of course, in extreme environments such as the Sun, no molecule is safe from destruction.

Chemical change : Chemical changes occur when the bonds between atoms in a molecule are created or destroyed.

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LaGreca ScienceUnit 2Chemistry Study Guide

There are 4 states of matter:

Each of these states is also known as a phase. Elements and compounds can move from one phase to another when specific physical conditions change. For example, when the temperature of a system goes up, the matter in the system becomes more excited and active. If enough energy is placed in a system, a phase change may occur as the matter moves to a more active state.

SOLID-

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LaGreca ScienceUnit 2Chemistry Study Guide

What is one physical characteristic of a solid? Solids can be hard like a rock, soft like fur, a big rock like an asteroid, or small rocks like grains of sand. The key is that solids hold their shape and they don't flow like a liquid. A rock will always look like a rock unless something happens to it. The same goes for a diamond. Solids can hold their shape because their molecules are tightly packed together.

In the same way that a large solid holds its shape, the atoms inside of a solid are not allowed to move around too much. Atoms and molecules in liquids and gases are bouncing and floating around, free to move where they want. The molecules in a solid are stuck in a specific structure or arrangement of atoms. The atoms still vibrate and the electrons fly around in their orbitals, but the entire atom will not change its position.

See below how tightly packed atoms are in solids!!

LIQUID

Liquids are found between the solid and gas states. Examples of liquids at room temperature include water (H2O), blood, and even honey. If you have different types of molecules dissolved in a liquid, it is called a solution. Honey is a solution of sugar, water, and other molecules.

Liquids fill the shape of any container they are in. If you pour water in a cup, it will fill up the bottom of

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LaGreca ScienceUnit 2Chemistry Study Guide

the cup first and then fill the rest. If you freeze that cup of water, the ice will be in the shape of the cup.

The top of a liquid will usually have a flat surface. That flat surface is the result of gravity pulling on the liquid molecules. Let’s go back to the cup for a moment. If you put an ice cube (solid) into the cup, it will sit there and not change shape. As the cube warms and melts, the liquid water will fill the bottom of the cup and have a flat surface on top.

Another trait of liquids is that they are difficult to compress. When you compress something, you take a certain amount of material and force it into a smaller space or volume. You force the atoms closer together. Most solids are very difficult to compress while gases are easier. You can find compressed gases in SCUBA air tanks. Liquids are in the middle, but tend to be difficult to compress because the molecules are already close together. You probably can’t compress a liquid with your hands. It takes a lot of force.

GAS

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LaGreca ScienceUnit 2Chemistry Study Guide

Gases are everywhere. You may have heard about the atmosphere. The atmosphere is an envelope of gases that surrounds the Earth. In solids, atoms and molecules are compact and close together. Liquids have atoms that are spread out a little more. The molecules in gases are really spread out, full of energy, and constantly moving around in random ways.

What is another physical characteristic of gases? Gases can fill a container of any size or shape. It doesn't matter how big the container is. The molecules spread out to fill the whole space equally. Think about a balloon. No matter what shape you make the balloon, it will be evenly filled with the gas molecules. Even if you make a balloon animal, the molecules are spread equally throughout the entire shape.

Liquids can only fill the bottom of a container, while gases can fill it entirely. The shape of liquids is very dependent on gravity, while less dense gases are light enough to have a more freedom to move.

PLASMAPlasmas are a lot like gases, but the atoms are different, because they are made up of free electrons and ions of an element such as neon (Ne). You don't find naturally occurring plasmas too often when you walk around. They aren't things that happen regularly on Earth.

http://kidsneedscience.tumblr.com/post/12196290467/plasma

https://www.youtube.com/watch?v=2osF6l6-zWg

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LaGreca ScienceUnit 2Chemistry Study Guide

To understand the difference between physical and chemical change:

When molecules move from one phase to another they are still the same substance. There is water vapor above a pot of boiling water. That vapor (or gas) can condense and become a drop of water in the cooler air. If you put that liquid drop in the freezer, it would become a solid piece of ice. No matter what physical state it was in, it was always water. It always had the same chemical properties.

On the other hand, a chemical change would build or break the chemical bonds in the water molecules. If you added a carbon (C) atom, you would have formaldehyde (H2CO). If you added an oxygen (O) atom, you would create hydrogen peroxide (H2O2). Neither new compound is anything like the original water molecule. Generally, changes in the physical state do not lead to any chemical change in molecules.

http://www.glencoe.com/sites/common_assets/science/virtual_labs/E03/E03.html

Heat is a source of energy that can change the state of matterwhich also causes particles in matter to gain kinetic energy.

What is Kinetic energy? Watch this to review it:

https://www.youtube.com/watch?v=IqV5L66EP2E

Temperature- Temperature is the property of matter which reflects the quantity of energy of motion of the component particles. There are several scales used to measure this value (e.g., Kelvin, Celsius, Fahrenheit).

melting point-the constant temperature that an object melts. The temperature increases and the atoms in an object vibrate faster. The molecules also move farther apart as the matter turns into liquid. (THINK ICE TURNS TO WATER)

boiling point-the temperature in which a liquid will turn into a gas or vapor. The temperature increases and the molecules move farther apart. (THINK LIQUID TO STEAM)

condensation point-the temperature in which a gas turns into a liquid. Heat is removed and the gas changes into a liquid (THINK DEW)

freezing point-the temperature in which a liquid turns into a solid. The temperature decrease and the atoms in an object vibrate slower. The molecules also move closer together as the liquid turns into a solid. (THINK WATER TURNS TO ICE)

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LaGreca ScienceUnit 2Chemistry Study Guide

IMPORTNT TO KNOW! If two objects that have the same elements and the same melting point have different masses (100g vs. 50g), the object with the smaller mass would melt faster, but the melting point would remain the same.

Evaporation- is the process by which water changes from a liquid to a gas or vapor. Water boils at 212 degrees F (100 degrees C), but it actually begins to evaporate at 32 degrees F (0 degrees C); it just occurs extremely slowly. As the temperature increases, the rate of evaporation also increases.

The amount of evaporation depends on the temperature, and it also depends on the amount of water there is to evaporate. For example, there is not much evaporation occurring in the Sahara Desert, but why? Although it can get extremely hot in the Sahara, it's just sand - there's just not much water to be evaporated.

Condensation- is the opposite of evaporation. It takes place when water vapor in the air condenses from a gas, back into a liquid form, and leaves the atmosphere, returning to the surface of the Earth.

http://study.com/academy/lesson/what-is-condensation-definition-examples-quiz.html

http://www.kidsgeo.com/geography-for-kids/0107-condensation.php

Sublimation- Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. An example of sublimation is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water.

http://study.com/academy/lesson/what-is-sublimation-in-chemistry-definition-process-examples.html

Part 3: Compare the independent and dependent physical properties of pure substances

Questions: What are the properties of different types of matter? What is a chemical property and a physical property? Why do some things float while others sink?

Matter can have different properties:

Chemical property-characteristics involved when a substance interacts with another substance to change its chemical make-up

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LaGreca ScienceUnit 2Chemistry Study Guide

Physical property-are used to identify, classify or describe matter. These are characteristic that can be observed using the 5 senses, WITHOUT changing the substance into something else.

http://examples.yourdictionary.com/examples-of-physical-properties.html

http://study.com/academy/lesson/matter-physical-and-chemical-properties.html

Solubility: a property of matter that can be observed without changing the identity of the matter

Solubility is the ability to dissolve into (become a part of) another substance. Something that dissolves, like the sugar in our example, is called a solute. The substance that it dissolves into, like the tea, is called the solvent. When a solute dissolves into the solvent, the end product is called a solution.

http://study.com/academy/lesson/solubility-lesson-for-kids-definition-rules.html

https://www.youtube.com/watch?v=zjIVJh4JLNo

https://www.youtube.com/watch?v=TglqdJ2CkHA

Solute-the substance that is dissolved in a solution. For example, salt when its dissolved in water.

Solvent-the substance the solute is dissolved in. For example, water when salt is dissolved.

Mass –a measure of how much matter is in an object. Mass is commonly measured by how much something weighs. But weight can change for different locations (such as on the moon) while the mass stays the same. Mass and weight are NOT always the same value!!!

TRY THIS-- MASS OR WEIGHT? https://www.mathsisfun.com/measure/weight-mass.html

Volume- the quantity of three-dimensional space occupied by a liquid, solid, or gas. Common units used to express volume include liters, cubic meters, gallons, milliliters, teaspoons and ounces.

Density

Density is a characteristic property of a substance. The density of a substance is the relationship between the mass of the substance and how much space it takes up (volume). The mass of atoms, their size, and how they are arranged determine the density of a substance. Density equals the mass of the substance divided by its volume; D = m/v. Objects with the same volume but different mass have different densities.

Weight-a measure of the gravitational force of matter

http://www.scienceforkidsclub.com/mass-and-weight.html

https://middleschoolscience.com/chemistry/properties-of-matter/

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