chemistry b midterm - short answers
how many neutrons are in an atom of 144/62 Sm?
82
how many electrons are in a neutral atom of 130/56 Ba?
130
what is the mass number of the atom 86/36 Kr?
86
how many protons are in an atom of 91/40 Zr?
91
arrange the following elements in order of increasing electron affinity (smallest to largest): Cl, Se, S, Cs, and Te
Cl, S, Se, Te, Cs
explain the difference between a pure substance and a homogeneous mixture. use an example in your explanation.
a homogeneous mixture can be separated by physical means, whereas a pure substance cannot. for example, salt can be removed from a salt-water mixture by evaporating the water, but to separate water into hydrogen and oxygen requires chemical means
why do atomic radii increase down a group and decrease across a period?
atom radii increases down a group because more energy levels are added while it decreases across a period because of increasing positive charge in the nucleus
how is electron affinity different from electronegativity?
electron affinity is the energy that occurs when a neutral atom gains an electron while electronegativity is the ability of an atom in a molecule to attract shared electrons to itself.
name three different way that mixtures can be separated.
filtration, distillation, and crystallization
which element has the highest electronegativity? why do you think it has the highest value?
fluorine and because it has the highest value because electronegativity increases from bottom to top in groups, and increases from left to right across period.
explain why hydrogen is unique among all the elements.
hydrogen has only one proton and on electron. this condition allows it to react with many other elements.
arrange the following atoms in terms of increasing atomic radius (from smallest to largest): Rb, Li, Cl, and K
idk
explain why it is incorrect to assume that all chemicals are potentially dangerous or hazardous. give two examples of chemicals that are necessary for human life
it is incorrect to assume that all chemicals are potentially dangerous because many are unresponsive or are needed to carry out basic functions of living things. examples: water, sucrose
distinguish between mass and weight.
mass is a measure of the amount of matter in an object, while weight is the force exerted on an object due to the acceleration of gravity
what are the SI standard units for length and mass? why isn't there a standard SI unit for volume?
the SI standard units for length and mass are meter and kilogram. volume is a derived unit and is calculated from length measurements.
which one of the following is not an SI unit for density - kg/m^3, g/cm^3, g/mL, or g/m^2? explain your answer.
the unit g/m^2 because density units must express mass per volume.
explain why flammability and combustibility are chemical properties
to observe either flammability or combustibility, a chemical change must occur. to observe either of these properties, something must burn and change to combustion products, such as water and carbon dioxide.
when water boils, steam forms. when vinegar and baking soda combine, carbon dioxide gas is released. which change is physical, and which is chemical? how do you know?
water boiling and steam forming would be a physical change because a physical change is a change in state, while the vinegar and baking soda combining and carbon dioxide being released would be a chemical change because in a chemical change, a new substance is released.
