PRINCIPLES OF CHEMISTRY 3 Flashcards
What is ionic bonding?
Ionic bonding occurs when a metal bonds with a non-metal. Transfer of elections.
Valence electrons are transferred from the metal atom (or atoms) to the non-metal atom (or atoms). The metal atoms form positive ions known as cations. The non-metal atoms form negative ions known as anions. Both types of ion have full outer electron shells and are stable.
What are examples of ionic bonding?
Sodium chloride
At room temperature, ionic compounds exist as crystalline solids. Strong electrostatic forces of attraction between the ions, called ionic bonds, hold the oppositely charged ions together in a regular, repeating, three-dimensional arrangement throughout the crystal. This forms a structure known as a crystal lattice.
Formula and names of ionic compounds?
Ionic compounds can be composed of ions formed from single atoms called monatomic ions or ions formed from small groups of atoms which are bonded together and called polyatomic ions, examples the ammonium ion NH4+ and the carbonate ion CO3 2-.
To name anions:
The name of an anion formed from a single atom is derived from the name of the element, with the ending -ide. Example N3- is the nitride ion. When oxygen is present in a polyatomic anion the name of the ion is derived from the element combined with the oxygen, with the ending -ite or -ate. Example NO2- is the nitrite ion and NO3- is the nitrate ion. Alternatively, the ending -ate is used with the oxidation number of the element given in brackets. Example NO2- is the nitrate(lII) ion and NO3- is the nitrate(V) ion.
When writing formulae of ionic compounds the sum of the positive charges and the sum of the negative charges must be equal. This is because the total number of electrons lost by one type of atom or group of atoms must be the same as the total number gained by the other type of atom or group of atoms. Formulae of ionic compounds are empirical formulae since they represent the ratio of ions present. They are also known as formula units.
Write the chemical formula of an ionic compound?
What is covalent bonding?
This occurs when two or more non-metals bond
Sharing of electrons.
Unpaired valence electrons are shared between the atoms which results in the formation of molecules. The shared electrons orbit around both atoms sharing them. This forms strong covalent bonds which hold the atoms together. Each shared pair of electrons forms one covalent bond. Covalent bonding can occur between atoms of the same element, example fluorine (F2). It can also occur between atoms of two or more different elements, example carbon dioxide (CO2). Seven common elements are composed of diatomic molecules in their free state: hydrogen (H2), oxygen (02), nitrogen (N2), fluorine (F2), chlorine (CI2), bromine (Br2) and iodine (I2). The formula of a covalent substance represents one molecule of the substance, therefore, it is the molecular formula. In many covalent compounds, the molecular and empirical formulae are the same, example water (H2O). In some they are not the same, example the molecular formula of glucose is C6H12O6 but its empirical formula is CH2O. Structural formulae can also be used to represent molecules. Each covalent bond is shown by a line between the two atoms.
Covalent substances are composed of individual molecules which can be either polar or non-polar due to the electronegativity of the atoms present. Electronegativity is a measure of how strongly atoms attract bonding electrons. Fluorine, oxygen, chlorine and nitrogen are the most electronegative elements.
In a polar molecule, one type of atom has a partial positive charge (delta+) and another type has a partial negative charge (delta-) because the atoms at either side of the covalent bond differ in electronegativity and attract the shared electrons with different strengths. Examples are water (H2O), ammonia (NH3), hydrogen chloride (HCI) and ethanol (C2H5OH).
In a non-polar molecule, the electronegativity of the atoms is similar or the same and they attract the shared electrons with equal strengths so the molecule does not have partially charged regions. Examples are hydrogen (H2), oxygen (O2) and methane (CH4).
The covalent bonds holding the atoms together in the molecules are strong. The molecules themselves are held together by intermolecular forces which are weak in polar substances and extremely weak in non-polar substances.
What are 3 main types of bonding?
- Ionic bonding
- Covalent bonding
- Metallic bonding - this occurs within metals
How are chemical compounds formed?
Chemical compounds are formed when elements bond by ionic or covalent bonding.
Why bonding?
Atoms of elements in Group 0 of the periodic table are stable and un-reactive and exist in nature as individual atoms because they have full outer electron shells or valence shells. Atoms of all other elements are not stable because they do not have full valence shells. These atoms attempt to obtain full valence shells and become stable by bonding with each other.
- Losing valence electrons to atoms of another element. Metal atoms with 1, 2 or 3 valence electrons usually lose their valence electrons and form positive cations.
- Gaining valence electrons from atom s of another element. Non-metal atoms with 5,6 or 7 valence electrons usually gain electrons into their valence shell and form negative anions.
- Sharing electrons in their valence shells with other atoms. When non-metal atoms with 4, 5, 6 or 7 valence electrons bond with each other, they share valence electrons and form molecules.
What is a chemical formula?
Chemical formulae can be used to represent compounds formed by ionic or covalent bonding. A chemical formula shows which elements are present in a compound and shows the ratio between the elements.
What are the three ways in which a chemical formulae can be written?
- The molecular formula. This gives the actual number of atoms of each element present in one molecule of a compound. For example, the molecular formula of ethene is C2H4
- The structural formula. This is a diagrammatic representation of one molecule of the compound. Lines between the atoms are used to represent bonds. For example, the structural formula of ethene.
C double bond C and 4 hydrogens - The empirical formula. This gives the simplest whole number ratio between the elements in the compound. Example the empirical formula of ethene is CH2
How to write empirical formula of compounds?
Using the concept of valence number or valency.
Valency is the number of bonds an atom can form when bonding with other atoms. It is determined by the number of valence electrons an atom has, and it can be thought of as the number of electrons an atom has to lose, gain or share when bonding.
To write the empirical formula of a compound formed from two elements. Determine the valencies of each element in the compound. Write the symbol of the first element. If a metal is present, always write its symbol first. Write the valency of the second element immediately after the symbol of the first element in subscript. Write the symbol of the second element immediately after the subscript. Write the valency of the first element immediately after the symbol of the second element in subscript. Note If a valency is 1, then no number is written as a subscript.
How to draw dot and cross bonding diagrams?
To draw dot and cross diagrams to show the formation of ionic and covalent compounds:
Decide if the compound is ionic or covalent. If it is formed from a metal and a non-metal it is ionic.
If it is formed from two or more non-metals it is covalent.
Determine the formula of the compound using the formulae of the ions, or valency.
Draw each atom in the formula, showing either all the electron shells or just the valence electrons. Use different symbols for electrons of each different type of atom, such as 0 and x.
Draw arrows to indicate electrons which are transferred or shared.• Redraw the ions formed after electrons have been transferred, or the molecule formed after
electrons have been shared. Do not forget to put the charges on all ions.
What is metallic bonding?
Metallic bonding occurs in metals. The metal atoms are packed tightly together in rows to form a metal lattice, and their valence electrons become delocalized. This means that the valence electrons are no longer associated with any specific atom and are free 10 move. This forms positive cations and a ‘sea’ of mobile electrons. The metal lattice is held together by the electrostatic forces of attraction between the delocalized electrons and the cations, known as the metallic bond, which is strong.
What are the four groups of solids?
- Ionic crystals
- Simple molecular crystals
- Giant molecular crystals
- Metallic crystals
What are ionic crystals?
An ionic crystal is made of an ionic lattice in which strong electrostatic forces of attraction called ionic bonds hold the cations and anions together in a regular, repeating, three-dimensional arrangement. Ionic crystals are represented by empirical formulae or formula units. Example Sodium chloride, empirical formula NaCI. Made of Na+ ions and CI- ions.
What are simple molecular crystals?
A simple molecular crystal is made of a molecular lattice in which weak forces of attraction called intermolecular forces hold small molecules together in a regular, three-dimensional arrangement. The atoms within each molecule are bonded together by strong covalent bonds. Simple molecular crystals are represented by molecular formulae.
Examples
- Ice, molecular formula H2O. Made of water molecules.
- Dry ice, molecular formula CO2. Made of carbon dioxide molecules.
- Iodine, molecular formula I2. Made of iodine molecules.
- Glucose, molecular formula C6H12O6. Made of glucose molecules.
