BASIC CHEMISTRY 1 ( MID TEST )

Mid Semester Test

Course             : Basic Chemistry
Credit              : 3 SKS
Lecturer           : Dr. Syamsurizal

( Chairani Adelia – RSA1C112016 )

Attention : Blog Version. You are permitted to accsess the internet and open books but not allowed to cooperate or cheat, when find out, it bring about fail. You answere could be upload at your blog. Time: 08.00 – 17.00 WIB.

1.      Pure subtance X is solid at room temperature. If the subtance is heated to 230^o C is melted gradually. If then cooled to room temperature, the liquid can not be frozen.

a.       Is it Possible X of an element or a compound. Explain it!

b.      Does it a chemical change occured ? If so can it be said to undergo an endotherm changing, based on the information provided?

c.       Can it be said that the liquid is an element, based on the information provided.

2.      When a candle that weight 10 g is burned in oxigen, carbon dioxide and water vapor formed by combustion the weight more than 10 g. Was this case match with the law of conservation of mass. Explain it!

3.      When carbon burns in oxigen under limited number, it will form two gaseous compounds. Suggest the way to differentiate the two compounds with one another.

4.      After Mendeleev compiled the periodic table, he concluded that the atomic weight of certain element was wrong ruling, and this conclusion was apparently correct. How Mendeleev was able to predist that several atomic weights were wrong? Why his predictions are not always right. Explain

5.      When an aqueous solution of mekuri chloride is added to an aqueous solution of silver nitrate, a white solid forms. Identify the white solid and write the balanced equation for the reactions that occurs.

Answer :

1.       A.  X is a compound. The compound is a combination of two elements or more are joined chemically by a certain ratio in each of the molecule. If the compounds in the melt with the heat will melt more mudah.Tapi it would cai, liquid hard freezes at the same temperature setting before him melt. If you want to make it freeze the requirement is much lower temperatures. Maybe the temperature below 0 ℃.

B.  chemical changes that occur can be called endothermic reactions. Endothermic reaction is a reaction that is accompanied by heat transfer from the environment to the system (heat absorbed by the system from its environment), characterized by a decrease in the ambient temperature around the system. Substance X are initially solid when heated at a temperature of 230 ℃ melting in the heat in the environment caused by the move to the substance, that substance will melt and the temperature of the substance to be higher than
the ambient temperature.

C.  I think it can be said fluid element, because the element is a constituent or the bottom of an element. Where the liquid element is the element that is composed of elements, such as when liquid is added hydrochloric acid with sodium hydroxide to form sodium chloride. ((HCl + NaOH à NaCl  ). for instance soy liquid while.

2.       The law of conservation of mass is' In a reaction, the mass of substances before reacting equal to the mass of the substance after reacting ". in this case the mass of wax in the fuel would be equal to the mass of wax before the fire. While the wax melts, it remains still wax, which changes only the shape alone. Candles will burn the gas and the amount of energy (heat and light). If the combustion products collected and weighed, certainly mass equal to the mass plus the mass of oxygen candles that are used in the arson. Thus, this case can be said to be in accordance with the law of conservation of mass.

3.       How to distinguish between the two compounds to each other by doing an experiment to see his or elements making up the difference. As such, research that generates data analysis that can be seen is a striking difference between the two compounds is gas so we can see the difference that occurs between the two. Perhaps as a qualitative experiment.

4.       Predictions are not always correct because, in the Mendeleev periodic system of elements such as hydrogen are deviations from the other elements are not described. In 1869, Dmitri Ivanovich Mendeleev Russian chemist nationality arrange 65 elements known at that time. Sort of increasing atomic mass of the element Mendeleev and chemical properties
At the same time, Julius Lothar Meyer made ​​the arrangement of elements such as dikernukakan by Mendeleyev. Just, Lothar Meyer arrange elements based on their physical properties. Although there are differences, but both result in the same grouping elements.
Mendeleev provide empty boxes to place elements of the time it has not been found, such as the element with mass number 44,, 68 72, and 100. Mendeleyev had predicted the properties of elements and it is a prophecy after the elements were discovered. The composition of elements Mendeleev perfected under the law and called the Mendeleev periodic system.
Mendeleev periodic system consists of a group (the element that is located in one column) and period (elements located in one line)

5.       HgCl2 + 2AgNO3 à Hg(NO3)2 + 2AgCl

STRUCTURE ATOM AND PERIODIC TRENDS ( CH 7 )

PERIODIC TRENDS

In chemistry, periodic trends are the tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements.

Atomic radius
The atomic radius is the distance from the atomic nucleus to the outermost stable electron orbital in an atom that is at equilibrium. The atomic radius tends to decrease as one progresses across a period from left to right because the effective nuclear charge increases, thereby attracting the orbiting electrons and lessening the radius. The atomic radius usually increases while going down a group due to the addition of a new energy level (shell). However, diagonally, the number of electrons has a larger effect than the sizeable radius. For example, lithium (145 picometer) has a smaller atomic radius than magnesium (150 picometer).^{[citation needed]} Atomic radius decreases from left to right across a period, and also increases from top to bottom down a group.

Ionization energy
The ionization potential is the minimum amount of energy required to remove one electron from each atom in a mole of atoms in the gaseous state. The first ionization energy is the energy required to remove one, the nth ionization energy is the energy required to remove the atom's nth electron, after the (n−1) electrons before it have been removed. Trend-wise, ionization energy tend to increase while one progresses across a period because the greater number of protons (higher nuclear charge) attract the orbiting electrons more strongly, thereby increasing the energy required to remove one of the electrons. Ionization energy and ionization potentials are completely different.^{[citation needed]} The potential is an intensive property and it is measured by "volt" ; whereas the energy is an extensive property expressed by "eV" or "kJ/mole".

As one progresses down a group on the periodic table, the ionization energy will likely decrease since the valence electrons are farther away from the nucleus and experience a weaker attraction to the nucleus's positive charge. There will be an increase of ionization energy from left to right of a given period and a decrease from top to bottom. As a rule, it requires far less energy to remove an outer-shell electron than an inner-shell electron. As a result the ionization energies for a given element will increase steadily within a given shell, and when starting on the next shell down will show a drastic jump in ionization energy. Simply put, the lower the principal quantum number, the higher the ionization energy for the electrons within that shell. The exceptions are the elements in the boron and oxygen family, which require slightly less energy than the general trend.

Atomic radius can be further specified as:

• Covalent radius: half the distance between two atoms of a diatomic compound, singly bonded.
• Van der Waals radius: half the distance between the nuclei of atoms of different molecules in a lattice of covalent molecules.
• Metallic radius: half the distance between two adjacent nuclei of atoms in a metallic lattice.
• Ionic radius: half the distance between two nuclei

Electron affinity
The electron affinity of an atom can be described either as the energy gained by an atom when an electron is added to it, or conversely as the energy required to detach an electron from a singly charged anion. The sign of the electron affinity can be quite confusing, as atoms that become more stable with the addition of an electron (and so are considered to have a higher electron affinity) show a decrease in potential energy; i.e. the energy gained by the atom appears to be negative. For atoms that become less stable upon gaining an electron, potential energy increases, which implies that the atom gains energy. In such a case, the atom's electron affinity value is positive.^[1] Consequently, atoms with a more negative electron affinity value are considered to have a lower electron affinity (they are more receptive to gaining electrons), and vice versa. However in the reverse scenario where electron affinity is defined as the energy required to detach an electron from an anion, the energy value obtained will be of the same magnitude but have the opposite sign. This is because those atoms with a high electron affinity are less inclined to give up an electron, and so take more energy to remove the electron from the atom. In this case, the atom with the more positive energy value has the higher electron affinity. As one progresses from left to right across a period, the electron affinity will increase.in this case, class 7a which has the highest electron affinity than the other groups. Reactivity elements of group 7 down from top to bottom in a group - fluorine is the most reactive and most non reactive iodine.

Electronegativity
Electronegativity is a measure of the ability of an atom or molecule to attract pairs of electrons in the context of a chemical bond. The type of bond formed is largely determined by the difference in electronegativity between the atoms involved, using the Pauling scale. Trend-wise, as one moves from left to right across a period in the periodic table, the electronegativity increases due to the stronger attraction that the atoms obtain as the nuclear charge increases. Moving down a group, the electronegativity decreases due to the longer distance between the nucleus and the valence electron shell, thereby decreasing the attraction, making the atom have less of an attraction for electrons or protons.

In the group 13 elements electronegativity increases from aluminium to thallium. In group 14 electronegativity of lead is higher than that of tin.

Metallic properties

Metallic property decreases across a period with increase in number of valence electrons as well as a decrease in atomic radius, and it increases down the group with increase in number of shells and atomic radius

Non-Metallic properties

Non-metallic property increases across a period and decreases down the group due to the same reason.

STRUCTURE ATOM ( CH 6 )

PARTICLE MATERIAL

The smallest part of matter called particles.

 

Some opinions about particles of matter:
1. According to Democritus, the distribution of matter is discontinuous (if the material is divided and continues to be divided then finally obtained the smallest particle that could no longer be divided = called Atom)
2. According to Plato and Aristotle, the distribution of matter is continuous (division can continue indefinitely)

Basic Postulates of Dalton Atomic Theory:
1) All matter is composed of minute particles called atoms
2) The element is composed of material similar atoms
3) Atoms of an element are identical but different from atoms of other elements (having different masses)
4) The compound is a material consisting of two or more types of atoms with a certain ratio
5) Atoms can not be created or destroyed and can not be converted to other atoms through chemical reactions normal. The chemical reaction is the rearrangement (reorganization) of the atoms involved in the reaction

  The downside of Dalton Atomic theory postulates:
1) Atom is not something that is not divided, but rather made ​​up of subatomic particles
2) Atoms of the same element may have different masses (called isotopes)
3) Atoms of an element can be changed into atoms of other elements through nuclear reactions
4) Some of the elements are not made ​​up of atoms instead of molecules

ATOMIC THEORY DEVELOPMENT
1). Atomic Model Dalton
a) Atom described as a very small solid ball.
b) Atoms are the smallest particles that can not be broken again.
c) Atoms of an element have the same same, while the atoms of different elements, different in mass and nature.
d) Compounds are formed when atoms combine with each other.
e) A chemical reaction is the reorganization of atoms, so there is no atom has changed due to chemical reactions.

Dalton's atomic theory is supported by the second law of nature, namely:
1. Law of Conservation of Mass (Lavoisier law): the mass of substances before and after the reaction is the same.
2. Keep Comparative Law (law Proust): comparison of mass elements that make up a substance is fixed.

Weakness Atomic Model Dalton:
1) Can not explain the difference between a single atom elements with other elements
2) Can not explain the electrical properties of materials
3) Can not explain how atoms bond together
4) According to Dalton's atomic theory of number 5, no atom has changed due to chemical reactions. Now it turns out the reactions of nuclear chemistry, an atom can change into other atoms.

2). Thomson Atomic Model
After the discovery of the electron by JJ Thomson, Thomson atomic model formulated which is a refinement of the atomic model of Dalton. According to Thomson:
a) Atoms consist of a positively charged material and in which the electrons are scattered (like raisins in raisin bread)
b) Atoms are neutral, the positive charge and negative charge the same amount

  3). Rutherford Atom Model
a) Rutherford found evidence that the atomic nuclei are positively charged, are smaller than the size of the atomic mass of an atom but almost entirely from the point masses.
b) Atoms consist of a positively charged nucleus and are at the center of the atom and the electrons move through the nucleus (like planets in the solar system).
c) Atoms are neutral.
d) The radius of the nucleus and atomic radii can be determined.

Weakness Rutherford Atomic Model:
Ø Inability to explain why the electrons do not fall into the nucleus due to electrostatic attractive forces the core to the electron.
Ø According to Maxwell's theory, if the electrons as charged particles around the core that has the opposite charge then the trajectory will spiral and will lose power / energy in the form of radiation and eventually fell to the core.

4). Niels Bohr Atom Model
• atomic model based on quantum theory to explain the spectrum of hydrogen gas.
• According to Bohr, the line spectrum indicates that the electrons only occupy certain energy levels in the atoms.
He said:
a) Atoms consist of a positively charged nucleus and the surrounding circulating electrons are negatively charged.
b) Electrons orbit around the nucleus of an atom in a particular orbit known as the stationary state of motion (fixed), hereinafter referred to as the main energy level (electron shell), which is expressed by the principal quantum number (n).
c) During the electrons are in a stationary orbit, its energy will remain so no light is emitted.
d) The electrons can only move from the lower stationary trajectory to a higher stationary trajectory if absorbing energy. Conversely, if the electrons move from a higher stationary trajectory to lower the release of energy.
e) In the normal state (without outside influence), the electrons occupy the lowest energy level (called the basic level = ground state)

Niels Bohr Atom Model Weaknesses:
1. Just to explain the spectrum of the atom or ion containing one electron and is not in accordance with the spectrum of electron atoms or ions that much.
2. Not being able to explain that atoms can form molecules through chemical bonds

5). Modern Atomic Model
Developed based on theories of quantum mechanics called wave mechanics; initiated by 3 experts:
a) Louis Victor de Broglie
Stating that the material has the properties of a material dualism, and as waves.
b) Werner Heisenberg
Put forward the principle of uncertainty for the material is of a particle and a wave. Distance or location of electrons that surround the nucleus can only be determined by the possibility - probability alone.
c) Erwin Schrodinger (refining models Bohr Atom)
Successfully prepared for electron wave equation using the principle of wave mechanics. Electrons surrounding the nucleus contained in an area that is 3-dimensional orbital around the nucleus where electrons with a specific energy can be found with the greatest possible.

Modern atomic models:
a) Atoms consist of a nucleus containing protons and neutrons while the electrons moving around the nucleus and are at particular orbitals of atoms that make up the skin.
b) the area of ​​the 3-dimensional orbital around the nucleus where electrons with a specific energy can be found with the greatest possible.
c) The position of electrons in the orbital-orbital quantum numbers stated.
• Orbital described as a cloud of electrons, namely: the forms of space where an electron is likely to be found.
• The meeting of the electron cloud, the more likely the electron was discovered and vice versa.