Convergent close-coupling (CCC) and Coulomb-Born with exchange and nor
malization (CBE) methods are used to study electron-impact excitation
of hydrogenlike ions. The nl-->n'l' cross sections demonstrate (i) goo
d agreement between the CCC and CBE results, (ii) a scaling over ion n
uclear charge z, (iii) a domination of the dipole (l'=l+/-1) contribut
ions in total n-->n' cross sections, and (iv) significant effect of el
ectron exchange in the energy range x<3 (here x is the ratio of the in
cident electron kinetic energy epsilon to the transition energy E(n,n'
)). For ions with z>5 the n-->n' cross sections obtained in the CCC an
d CBE approximations agree with each other to better than 10% for any
x. An accuracy of the cross sections scaling over z(4) depends on z: f
or z=6-18 the scaling is accurate to better than 10% (quantitative ana
lysis is done for n'<7), for ions with z<6 the cross sections deviate
from the z(4) scaling more significantly (at n about unity). The n-->n
' cross sections are presented by a formula which fits our CCC and CBE
results with an accuracy to better than 10% (for transitions with n<n
'<7 in ions with z>5). The new Gaunt factor G(x) suggested for the wid
ely used Van Regemorter formula [Astrophys. J. 136, 906 (1962)] makes
this formula accurate to better than 50% in the x>3 range and to bette
r than 20% in the x>100 range. It is shown that the semiempirical form
ula by Vainshtein, Sobelman, and Yukov [Electron-impact Excitation Cro
ss Sections of Atoms and Ions (Nauka, Moscow, 1973)] provides an accur
acy to better than 50% for any incident electron energy. For x<2 this
formula is accurate to better than 30%. These accuracy assessments are
based on a comparison with our CCC and CBE results.