Chemical Reactions Flashcards
Valence Electron
An electron in an outer orbital that can form bonds with other atoms.
Reactants
In a chemical equation, the substances on the left side of the equation, the starting materials in a chemical reaction.
Products
In a chemical equation, the substances on the right side of the equation, the substances that are formed in a chemical reaction.
Valence Electrons I
Electrons of the outermost shell of an atom are called valence electrons, and they have the highest energy. These electrons are readily transferred or shared during chemical reactions than those in the interior. Transfer or sharing electrons with another atom achieves the noble gas configuration by having eight electrons in the outermost shell and become stable. This plays an important role in chemical reactions.
Valence Electrons II
The number of valence electrons an element has can be based on its group in the periodic table. Elements in the same group in the periodic table have the same chemical behavior because they have the same number of valence electrons. Ex: Group IA elements, like Sodium and Potassium, have one valence electron. Neighboring group IIA such as magnesium and calcium have 2 valence electrons.
Valence Electrons III Leftside of Periodic Table
Elements on the left side of the periodic table have very low ionization energies (the energy required to remove the most loosely held electron) and low electronegativity (the tendency to attract electrons). These elements are classified as metals and usually lose electrons to another atom during a chemical reaction. IA lose one valence electron leaving imbalance in the number or protons to electrons, resulting in positive cations with a+1 charge, with outermost shell similar to noble gas. Ex: Na loses the only electron in its valence shell, Na+ ion has same number of electrons as neon (Ne) and is more stable. Magnesium loses 2 electrons forming Mg 2+ and has same number and configuration of electrons as Ne.
Valence Electrons VI on the Right Side of the Periodic Table
Elements on the right side of the periodic table, groups VIA and VIIA, gain electrons in chemical reactions. These have high ionization energies and can significantly draw valence electrons from other atoms towards themselves. Elements in Group VIIA: Fluorine (F), Chlorine (Cl), and Bromine (Br) gain one electron and end up with more electrons than protons in the nucleus, becoming negative anions with a a-1 charge (F-,Cl-,Br-). Because they end up with the same number of electrons as the noble gas, they achieve stability. Ex: VIA elements Oxygen (O) and Sulfur (S) gain 2 electrons O2 and S2 ions and noble gas valence electron configurations for stability.
Elements in the Periodic Table are
Elements group and placement in the periodic table will determine whether an element will gain, lose or share valence electrons. Elements on the left side of the periodic table with low ionization energies and low electronegativity are metals, which will tend to lose electrons and become and become cations. Electrons lost by metals are gained by elements on the right side of the periodic table, which have high electronegativities, a high affinity for them are nonmetals. Nonmetals gain electrons to become negatively charged anions. They will gain, lose and share electrons. Two or more nonmetals react they become stable by sharing electrons.
Covalent and Ionic Bonds I
Chemical bonds occur when two or more atoms have interactions between their valence electrons. Ionic bonds can form when there is a large difference in electronegativity, such as what exists between metals and nonmetals. Transfer of electrons from the metal to the nonmetal. They become ions or charged atoms. Metals are positively charged Cations and Nonmetals become negatively charged Anions. Ex: Sodium (Na+) becomes positively charged because it has lost an electron to the nonmetal Fluorine (F-) becomes negatively charged because it has gained an electron. These opposite charged ions attract one another, forming an ionic bond making Sodium Fluoride (NaF). Metals found on the left side and Nonmetals found on the right side of the periodic table.
Covalent and Ionic Bonds II
Elements also share electrons instead of transferring electrons, forming Covalent Bonds. Covalent bonds require sharing of electrons between two nonmetals. Not a sufficient difference in electronegativity to gain or lose electrons. Difference in electronegativity with covalently bonded molecules cause them to be polar or nonpolar. Polar covalent compounds have a negatively charged side and a positively charged side. Water is a polar molecule; Hydrogen side is partially positively charged and oxygen side is partially negatively charged. Results in a strong electronegativity of oxygen pulling at the shared electrons. These polar covalently bonded molecules are neutral in overall charge.
Chemical Reactions
Chemical Reactions are represented by chemical equations. Chemical eqautions have a basic layout going from left to right. Reactions on left ->Products on right
Reactants and Products
Formation of table salt is an example of a chemical equation. 2Na+Cl2->2NaCl. In this reaction, sodium and chlorine are the reactants and the ionic compound Sodium Chloride is the product.
Combustion Reaction
CH4 +2O2 -> CO2 + 2H20. Methane CH4 and O2 Oxygen are reactants. The products are water H20 and carbon dioxide C02. Coefficients help adjust quantities in the reaction, so that equal numbers of atoms of each element in the reactants are also in the product so the reaction is balanced.
Balancing Chemical Equations I
During a chemical reaction there is a change in the. bonding between atoms that occurs, but the total mass of the elements entering and exiting the reaction does not change. Chemical equations must be shown balanced equations, meaning there must be the same numbers of each element on both sides. In the combustion reaction , the equation should show identities but not quantities of reactants and products like this: CH4 + O2 -> CO2 + H20.
Balancing Chemical Equations II
CH4 + 2O2 -> CO2 + 2H20. Two hydrogen atoms are destroyed and an oxygen atom is created going from reactants to products, and so the equation is unbalanced. If a coefficient 2 is placed in front of oxygen O2, means two oxygen molecules react with methane CH4. Coefficient 2 infront of water H2O molecule in the product means the reaction forms two water molecules instead of one. Chemical reaction is now balanced here. CH4 +2O2 -> CO2 + 2H20. Same number of atoms for each element are present on both sides.
