TEAS SCIENCE 21 - CHEMISTRY

ATI TEAS SCIENCE REVIEWCHEMISTRYATI TEAS SCIENCE – CHEMISTRYQuestions related to chemistry test your knowledge of chemicalproperties and processes. You may be asked questions about states ofmatter, properties of matter, phase changes, chemical bonds, chemicalsolutions, chemical reactions, and acids and bases. You may be asked tobalance chemical equations.Let’s get started in understanding how chemistry is important on theATI TEAS.ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING STATES OF MATTERMatter is made up of microscopic particles that move different speedsdepending on the energy they are exposed to. We measure this energyas temperature. The molecules can move either quickly and randomlyor hardly at all.When the energy is high, matter take the form of a gas, in whichmolecules are moving about quickly and are far apart. Gases have nofixed form. Molecules are free to move at random past each other, andthey tend to fill any container that holds them. If a gas is not contained,its molecules will disperse.PHOTO CREDIT: LIVE SCIENCE

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING STATES OF MATTERLower temperatures result in a liquid, in which molecules cohere butare fluid. Coherence means that the molecules remain close together,but they can change position by sliding over one another. In liquids,molecules move less freely than in a gaseous state, sliding past oneanother. They have a fixed volume but will flow freely unless they fill aportion of a container.When the temperature is low, matter takes the form of a solid, in whichmolecules are packed closely together and retain their positions. Solidmatter is rigid, and molecules retain a uniform spacing. A solid has adefined form, which is brittle. It can be broken into pieces but tends tostay together.PHOTO CREDIT: LIVE SCIENCEA somewhat unusual state of matter is plasma, which is like a gas inmany of its properties but carries an electric charge.The TEAS focus on solids, liquids, and gases.ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHANGES IN STATE OF MATTERThe state of matter depends on temperature and pressure. Highertemperatures cause molecules to energize and move farther apart.Increasing pressure forces molecules closer together. Melting is thephase change from solid to liquid and boiling is the phase change fromliquid to gas. There is also a direct change from solid to gas known assublimation. The phase change from gas to liquid is condensation andthe change from liquid to solid is freezing. A direct change from gas tosolid is deposition.PHOTO CREDIT: VECTORSTOCKATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING PROPERTIES OF MATTERAll types of matter can be described in terms of the physicaland chemical properties each substance has. Physicalproperties are observable and there is an extensive list ofphysical properties that one could observe about a substance.A few examples are density, the temperatures at which ductivity, specific heat capacity, mass, volume, color, andmany other properties. Physical properties are further dividedinto intensive and extensive properties. An intensive propertydoes not depend on the size or amount of matter in theobject, while an extensive property does depend on theamount of matter in the object. For example, mass isextensive because the measurement would change the size ofthe sample. Boiling point is intensive because thetemperature at which the object boils is not dependent on itsvolume.PHOTO CREDIT: THOUGHTCO

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING PROPERTIES OF MATTERWater is a polar inorganic compound that is transparent andnearly colorless. H2O is a covalent compound because oxygenand hydrogen are nonmetals. It has 8 total valence electrons(6 from oxygen and 1 from each hydrogen). Breaking thebonds requires a lot of energy, so water has a very highspecific heat and heat of vaporization. The molar mass ofwater is 18.02 g/mol. It commonly exists as solid, liquid, andgas.PHOTO CREDIT: SLIDESHAREATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING PROPERTIES OF MATTERThe polarity of water allows it to exhibit both cohesive andadhesive properties. Cohesiveness allows water to travelthrough tiny capillaries and creates surface tension on thesurface of a body of water. Adhesiveness allows water to stickto other molecules and dissolve them, making it known as the“universal solvent.”PHOTO CREDIT: BIONINJAATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING PROPERTIES OF MATTERWater also has a unique property called osmosis, which is aspecific type of diffusion. Diffusion is a term used to describethe process of a substance moving from an area of highconcentration to an area of low concentration. Osmosis is atype of diffusion in which water moves passively through asemi-permeable membrane to equalize water concentrationon both sides of the membrane. This is how water movesthrough cell walls in the body.PHOTO CREDIT: BYJU

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL BONDSA chemical compound is created when two or more atomsjoin to form a chemical bond that leaves the atoms in a lessexcited state than they were in before the bond. Such bondsform in two ways.PHOTO CREDIT: SHUTTERSTOCKATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL BONDSA covalent bond occurs when atoms share electrons between them. This type of bond iscommon between two atoms of the same element, as in hydrogen (H2) or in similarelements. When a molecule shares a pair of electrons in a stable state, it has formed acovalent bond. Alkanes, for example, share a single bond. In some compounds, one atomtakes the shared electron for more time, due to its structure, forming a polar covalentbond. This molecule is partly negatively charged and partly positively charged. Somemolecules form a double bond, sharing four electrons as opposed to two. These bondsare commonly represented in the alkenes, hydrocarbons with twice as many hydrogenmolecules as carbon molecules. It is possible to form triple bonds as seen in a group ofhydrocarbons called alkynes.PHOTO CREDIT: BRITANNICAPHOTO CREDIT: QUORAATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL BONDSAn ionic bond is created between atoms when one atom gives an electron to the other.These bonds typically take place between metals and nonmetals due to the uniqueelectron configuration of metals, with the metal giving an electron to the nonmetal. Thistransfer creates a positive charge and a negative charge at the ends of the compound.The positive charge, or cation, is created by the giver of an electron. The negative charge,or anion, is located at the receiving end of the electron. The net charge of thecompounds remains balanced at zero.PHOTO CREDIT: WIKIBOOKS

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL SOLUTIONSA chemical solution is a group of chemical compounds evenly distributed in a state ofmatter. The solution is a homogenous mixture where one chemical compound iscompletely dissolved in the others. This is most easily achieved in a liquid state. There aremixtures that are not solutions. A heterogeneous mixture maintains separation betweentwo substances, like oil and water.ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL SOLUTIONSThe solute is the compound dissolved in the solvent. Liquids make excellent solvents.The solubility of a solvent depends on the nature of the liquid as well as external factorslike temperature. The concentration of the solution is the amount of solute in thesolution. The mole is the unit of measurement for chemical reactions and refers to acompound’s molecular mass.ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL REACTIONSTo create a new chemical compound from other elements andcompounds, a chemical reaction is needed. Two or more reactants areadded together, often with an input of energy, creating one or moreproducts and by-products. Photosynthesis occurs, for instance, when aplant cell combines carbon dioxide and water. The sun’s rays providethe energy. The chemical reaction produces sugar and oxygen.Chemical reactions are shown with equations and have a basicpattern: reactants go on the left and products go on the right, with thereaction sign (an arrow) showing the direction of the reaction in themiddle. Here is an example showing the direction of the reaction inthe middle. Here is an example showing the formation of watermolecules:2"# %# 2"# %Equations for chemical reactions must be balanced; there must be thesame number of atoms of each element on both sides of the reaction.Notice in the equation above that there are four hydrogen atoms andtwo oxygen atoms on each side. Only their arrangement is changed.PHOTO CREDIT: CHEMISTRY LIBRETEXTS

ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL REACTIONSThere are five basic types of chemical reactions: Synthesis: two separate things joining together to form 1compound Decomposition: 1 compound breaks down into 2 or morecompounds Combustion: The use of fuel (combustible material) withoxygen to form carbon dioxide and water Single replacement: 1 element or compound replacesanother element or compound in a compound PHOTO CREDIT: CHEMISTRY LIBRETEXTSFor example: A BC AC B Double replacement: 2 ionic compounds create two moreiconic compounds For example: AB CD AD CBATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL REACTIONSReaction rates depend on the likelihood of collision between particles.The reaction rate can be altered by changing the following factors: Concentration – The more particles there are, the higher the chance ofcollisions. Temperature – Particles excite at higher temperatures, so morecollisions are likely and will have more energy. Pressure – Increased pressure forces particles together, so collisionsare more likely Surface area – In a solid, only particles at the surface can collide. Thebigger the surface, the faster the reaction. Breaking up a sample intosmaller particles provides more surface area for collisions. Catalysts – A catalyst is a substance that changes the rate of a chemicalreaction but is chemically unchanged at the end of the reaction.ATI TEAS SCIENCE – CHEMISTRYUNDERSTANDING CHEMICAL REACTIONSChemical reactions occur in nature and in the laboratory. A catalyst willspeed up the reaction by lowering the amount of energy needed tostart the reaction. Enzymes act as catalysts in cellular processes. Theyquicken the chemical reaction, turning a molecule, known as asubstrate, into a product without being altered themselves.PHOTO CREDIT: BIONINJA