Teas STUDY (S.3.3 - Describe Chemical Reactions)

Which of the following sets of coefficients balances the following chemical reaction? ______ N2 + ______ H2 → ______ NH3​​​​​​​

1, 3, 2 It works out to a total of (nitrogens) and (hydrogens) on each side of the reaction.

Which of these elements have the same number of valence electrons and similar chemical properties as strontium (Sr)? Use the periodic table to help you answer the question.​​​​​​​

A Magnesium (Mg) Elements in the same group have similar properties and the same number of valence electrons.

The 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 _______________ compound sodium chloride is the product.

ionic

Based on an element's group and placement in the periodic table, a trend can be observed to 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 _____________, which will tend to _______________ electrons and become ______________. The electrons lost by metals are gained by elements on the right side of the periodic table, which have high electronegativities—that is, a high affinity for them—and are ________________. Nonmetals _____________ electrons to become negatively charged ___________. Reactions between elements with similar tendencies to gain or lose electrons will tend to share electrons with each other. For example, when two or more nonmetals react, they become stable by sharing valence electrons.

metals lose cations nonmetals gain anions

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 ________ change. Chemical equations must be shown as __________ equations, meaning there must be the same numbers of each element on both sides. Looking at the combustion reaction again, the equation could have simply shown the identities but not the quantities of the reactants and products, like this: CH4 + O2 → CO2 + H2O​​​​​​​

not balanced

Group IA elements lose ____________ valence electron, leaving an imbalance between the number of positive protons in the nucleus and electrons, resulting in positive cations with a +1 charge, with an outermost shell similar to a noble gas. For example, sodium (Na) loses the only electron in its valence shell, so now the Na+ ion has the same number of electrons as neon (Ne) and therefore is more stable. Magnesium (Mg) can lose 2 valence electrons, forming Mg2+, which also has the same number and configuration of electrons as Ne.

one

Group IA elements—such as sodium and potassium—have ___________valence electron. The elements in the neighboring group, IIA—such as magnesium and calcium—have ______________ valence electrons. Typically, elements on the left side of the periodic table have relatively low ___________________________(the energy required to remove the most loosely held electron) and low ____________________________(the tendency to attract electrons). These elements are classified as _______________ and usually _______________ electrons to another atom during a chemical reaction.

one two ionization energies electronegativity metals lose

Water is a __________ molecule; the hydrogen side of the molecule is partially ____________ charged, and the oxygen side is partially _____________ charged. This is a result of the strong electronegativity of oxygen pulling at the shared electrons. These polar covalently bonded molecules are still neutral in overall charge.

polar positively negatively

Sometimes elements share electrons instead of transferring electrons, forming a different type of bond. Covalent bonds require the ______________ of electrons and occur between two ________________. In covalent bonds, there is not a sufficient difference in electronegativity to gain or lose electrons. However, differences in electronegativity within a covalently bonded molecule cause them to be _______________ or ____________. Polar covalent compounds have a ____________ charged side and a ____________ charged side.

sharing nonmetals polar nonpolar negatively positively

Chemical bonds occur when two or more atoms have interactions between their _____________________ electrons. Ionic bonds can only form when the elements involved have a large difference in ____________________, such as exists between metals and nonmetals. This difference allows for the transfer of electrons from the metal to the nonmetal. These elements then become ions or charged atoms. As mentioned earlier, metals tend to become _____________ charged cations, and nonmetals become __________________ charged anions.

valence electronegativity positively negatively lost left right

The electrons of the outermost shell of an atom are called__________________, and they have the ________________. These outer electrons are more readily transferred or ______________ during chemical reactions than those in an atom's interior. Transfer of the electron to another atom or sharing these electrons with another atom allows the atom to achieve the _______________________________ by having ____________ electrons in the outermost shell and become ____________. Because of this, valence electrons play an important role in chemical reactions.

valence electrons highest energy shared noble gas electron configuration eight stable

mole

A unit of a substance that is equal to exactly 6.02214076 × 10 particles of that substance

valence electron

An electron in an outer orbital that can form bonds with other atoms

How many oxygen atoms are present on each side of the following reaction? 2C2H18+25O2 → 16CO2+18H2O​​​​​​​

C 50 There are 50 on the left (25 × 2) and 50 on the right (16 × 2 + 18).

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

Take a look at an example of a combustion reaction. CH4 + 2O2 → CO2 + 2H2O​​​​​​​

Methane (CH4) and oxygen (O2) are the reactants. The products are water (H2O) and carbon dioxide (CO2).

chemical equation

Mathematical representation of a chemical reaction

Which of the following substances are ionic compounds?​​​​​​​

NaCl​​​​​​​ K (potassium) and sodium (Na) are metals, and Cl (chlorine) is a nonmetal. D KCl K (potassium) and sodium (Na) are metals, and Cl (chlorine) is a nonmetal.

Chemical reactions are represented by chemical equations. Chemical equations have a basic layout going from left to right: reactants, reaction sign showing the direction of the ____________ (→), and ______________.

Reactants → Products​​​​​​​

The elements in the upper right side of the periodic table, such as those in groups VIA and VIIA, tend to _________________ electrons in chemical reactions. These elements have high _____________________________ and a significant ability to draw valence electrons from other atoms toward themselves. Elements in Group VIIA—such as fluorine (F), chlorine (Cl), and bromine (Br)—gain one electron and thus end up with more _________________ than the number of protons in the nucleus, becoming _____________________ anions with a -1 charge (F-, Cl-, and Br-). Because they end up with the same number of electrons as the neighboring noble gas, they achieve stability. Group VIA elements oxygen (O) and sulfur (S) gain 2 electrons, forming O2- and S2- ions and noble gas valence electron configurations for stability.

gain ionization energies electrons negative

The number of valence electrons an element has can be determined based on its ____________________ in the periodic table. Although the periodic table was originally assembled based on chemical behavior of the elements before their atomic structure was known, it turned out that elements in the same group in the periodic table have the same chemical ____________ because they have the same number of _______________________.

group behavior valence electrons

Chemical reactions occur constantly to____________ and _________ bonds between elements and compounds. Elements in the same group in the periodic table undergo similar chemical reactions due to shared valence electron number. For this TEAS task, you need to be able to describe chemical bonding and reactions, recognize the role of valence electrons in bonding, know how to balance a chemical reaction, and understand how quantities of reactants and products are represented in a chemical reaction.

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